J. River's MC and its FLAC decoder uses 'DISC #' rather than DISCNUMBER for FLAC files. The following (and attached) patch translates this to SlimServer's internal DISC tag.

--- Slim/Formats/FLAC.pm 2006-05-18 01:02:52.000000000 -0700
+++ Slim/Formats/FLAC.pm.new 2006-05-18 11:21:38.000000000 -0700
@@ -43,6 +43,7 @@
# J.River once again.. can't these people use existing standards?
   'REPLAY GAIN' => 'REPLAYGAIN_TRACK_GAIN',
   'PEAK LEVEL' => 'REPLAYGAIN_TRACK_PEAK',
+  'DISC #' => 'DISC',
);

my @tagNames = qw(ALBUM ARTIST BAND COMPOSER CONDUCTOR DISCNUMBER TITLE TRACKNUMBER DATE);


I've tested it, and it works for me. Is it possible that someone might check in this one-liner?