While trying to work around a user interface bug in Backup Exec 2012, I tried to recreate a custom report duplicating the list of all backup sets on a device (in my case, a big back-up-to-disk folder). I found that it wasn't really possible. 

• The most annoying part is that a separate (identical) line is produced for every backup-to-disk file in a backup set.  You can't see the backup to disk files (and I don't want to) so this is just noise.  The custom reports don't have a way to summarize or consolidate fields; all grouping accomplishes is inserting extra headers.
• One of the media group fields is "Resource ID". "Resource name" would be far more useful.   I'm sure I can cross-reference that with some other report that names each resource, but this is a reporting tool, intended to produce easily-readable end product reports.  Perhaps for future jobs, I will be able to modify the backup job properties to put the resource name in the backup set name.
• If I have to combine and cross reference data to get the report I want, a CSV file would be better than a formatted report.   This is a good idea in general, because that way, Symantec won't have to think of absolutely every way somebody might want to report data.
• The ultimate solution of my particular need would be to add a catalog view (and corresponding field group) to custom reports.