Actually there is no means to change debriefing music in FRED2. All you can do is add .wavs for any voice acting you have. FS2 automatically plays one of three tracks (FS2_DB_01/02/03.wav)during debrief, depending on whether you did excellent, barely won, or failed. What you might have run into was one of the debriefing themes being used for briefing, since that *is* possible - though I don't know if it's actually done anywhere in Inferno. If you still want to modify the themes played during debriefing, you can either go talk to the SCP people, or you can replace the existing themes with three of your own by the same names, in which case FS2 should use those instead.
