If you do provide this feature (and I hope you do), you might also consider the case when tracks needing grouping span multiple CDs of a boxed set, e.g., composer #1/opus #1 is on all the tracks of CD1 plus the first few tracks of CD2, and composer #2 / opus #2 is on the remaining tracks of CD2. As an example, see "Berlioz: Requiem; Boito: Prologue to Mefistofele" on amazon.com. Doesn't happen much (and we can handle the way BLOWERS suggests, although I had to add two custom fields to reference back to the physical CD). I would be willing to settle just for the vanilla situation, however -- would make life much easier.

Bill