diff --git a/docs/environment-variables.md b/docs/environment-variables.md
index 9682fdf9..db5923a4 100644
--- a/docs/environment-variables.md
+++ b/docs/environment-variables.md
@@ -1441,7 +1441,7 @@ Delay between requests in seconds to avoid rate limiting (0-10).
 | `IRC_CHANNEL` | Channel name without the # prefix. Used for all searches unless a separate audiobook channel is configured below. | string | _none_ |
 | `IRC_NICK` | Your IRC nickname (required). Must be unique on the IRC network. | string | _none_ |
 | `IRC_SEARCH_BOT` | The search bot to address queries to (required). Searches are sent as "@<bot> <query>". | string | _none_ |
-| `IRC_AUDIOBOOK_CHANNEL` | Optional. Channel name (without the # prefix) to use for audiobook searches. Leave blank to use the main channel above for audiobooks too. | string | _none_ |
+| `IRC_AUDIOBOOK_CHANNEL` | Optional. Channel name (without the # prefix) for networks that index audiobooks separately, such as Undernet's bookz. Leave blank (the usual setting) to search the main channel above for audiobooks too. | string | _none_ |
 | `IRC_AUDIOBOOK_SEARCH_BOT` | Optional. Search bot for the audiobook channel. Leave blank to reuse the main search bot above. Only used when an audiobook channel is set. | string | _none_ |
 | `IRC_CACHE_TTL` | How long to keep cached search results before they expire. | string (choice) | `2592000` |
 
@@ -1510,7 +1510,7 @@ The search bot to address queries to (required). Searches are sent as "@<bot> <q
 
 **Audiobook channel**
 
-Optional. Channel name (without the # prefix) to use for audiobook searches. Leave blank to use the main channel above for audiobooks too.
+Optional. Channel name (without the # prefix) for networks that index audiobooks separately, such as Undernet's bookz. Leave blank (the usual setting) to search the main channel above for audiobooks too.
 
 - **Type:** string
 - **Default:** _none_
diff --git a/readme.md b/readme.md
index c50e8837..cdb2c07a 100644
--- a/readme.md
+++ b/readme.md
@@ -123,7 +123,7 @@ See the full [Environment Variables Reference](docs/environment-variables.md) fo
 Some of the additional options available in Settings:
 - **Prowlarr** - Configure indexers and download clients to download books and audiobooks
 - **Additional audiobook sources** - Configure additional sources for audiobook discovery
-- **IRC** - Add details for IRC book sources and download directly from the UI
+- **IRC** - Add details for IRC book sources and download directly from the UI. Most networks serve audiobooks from the same channel as ebooks (on `irc.irchighway.net` that's `#ebooks`, while `#bookz` is effectively inactive), so leave the separate audiobook channel blank unless your network actually indexes one. IRC audiobooks usually arrive as ZIP/RAR archives — keep those enabled under Supported Audiobook Formats or the releases are filtered out of results
 - **Library Link** - Add a link to your Calibre-Web or Grimmory instance in the UI header
 - **File processing** - Customiseable download paths, file renaming and directory creation with template-based renaming
 - **Network Settings** - Custom proxy support (SOCKS5 + HTTP/S) and configurable DNS
diff --git a/shelfmark/release_sources/irc/settings.py b/shelfmark/release_sources/irc/settings.py
index a0cf74ec..166056ca 100644
--- a/shelfmark/release_sources/irc/settings.py
+++ b/shelfmark/release_sources/irc/settings.py
@@ -102,10 +102,13 @@ def irc_settings() -> list[SettingsField]:
             key="audiobook_heading",
             title="Audiobooks",
             description=(
-                "Some networks index audiobooks in a separate channel from ebooks "
-                "(for example #ebooks for ebooks and #bookz for audiobooks). "
-                "Configure that channel here to search it for audiobook requests. "
-                "Leave these blank to search the main channel above for both."
+                "Most networks index audiobooks in the same channel as ebooks, so leaving "
+                "these blank is the right setting for almost everyone. On irc.irchighway.net "
+                "the audiobooks are in #ebooks and #bookz is effectively inactive — pointing "
+                "this at an empty channel just returns no results. Only fill these in when "
+                "your network really does index audiobooks elsewhere (Undernet's #bookz, for "
+                "example). Audiobooks are usually posted as archives, so keep ZIP and RAR "
+                "enabled under Supported Audiobook Formats or the releases are filtered out."
             ),
         ),
         TextField(
@@ -113,8 +116,9 @@ def irc_settings() -> list[SettingsField]:
             label="Audiobook channel",
             placeholder="e.g. bookz",
             description=(
-                "Optional. Channel name (without the # prefix) to use for audiobook "
-                "searches. Leave blank to use the main channel above for audiobooks too."
+                "Optional. Channel name (without the # prefix) for networks that index "
+                "audiobooks separately, such as Undernet's bookz. Leave blank (the usual "
+                "setting) to search the main channel above for audiobooks too."
             ),
             required=False,
             env_supported=True,
diff --git a/shelfmark/release_sources/irc/source.py b/shelfmark/release_sources/irc/source.py
index 46336d2e..6ee134b5 100644
--- a/shelfmark/release_sources/irc/source.py
+++ b/shelfmark/release_sources/irc/source.py
@@ -240,11 +240,11 @@ class IRCReleaseSource(ReleaseSource):
         nick = _config_text("IRC_NICK")
         search_bot = _config_text("IRC_SEARCH_BOT")
 
-        # Audiobooks may be indexed in a separate channel from ebooks on some networks
-        # (e.g. #ebooks for ebooks, #bookz for audiobooks). When an audiobook channel is
-        # configured and an audiobook was requested, route the search there (with its own
-        # search bot if set). Otherwise fall back to the main channel/bot, which keeps the
-        # single-channel networks that index both formats working unchanged.
+        # A few networks index audiobooks in a separate channel from ebooks (Undernet's
+        # #bookz, say). When an audiobook channel is configured and an audiobook was
+        # requested, route the search there (with its own search bot if set). Otherwise
+        # fall back to the main channel/bot — that is the common case, since most networks
+        # (irchighway included) serve both formats from the one channel.
         if is_audiobook(content_type):
             audiobook_channel = _config_text("IRC_AUDIOBOOK_CHANNEL")
             if audiobook_channel:
diff --git a/shelfmark/release_sources/newznab/source.py b/shelfmark/release_sources/newznab/source.py
index 2e2da599..8f258545 100644
--- a/shelfmark/release_sources/newznab/source.py
+++ b/shelfmark/release_sources/newznab/source.py
@@ -111,11 +111,12 @@ def _resolve_content_type(
     ranges, so trust the searched content type when the result carries a category we
     explicitly asked for.
     """
-    detected = _detect_content_type_from_categories(categories, content_type)
+    category_list = list(categories) if isinstance(categories, (list, tuple)) else []
+    detected = _detect_content_type_from_categories(category_list, content_type)
     if (
         detected == "other"
         and searched_categories
-        and _result_category_ids(categories) & set(searched_categories)
+        and _result_category_ids(category_list) & set(searched_categories)
     ):
         return "audiobook" if content_type == "audiobook" else "book"
     return detected