Do you mean the patches sound different in performance mode then they do in patch mode?
This has to do with EFX/Chorus/Reverb and tone output assignments. If this is the case then it's no suprise - this is typical with most synths. An XP-60 performance should be able to be programmed so that 1 channel can sound exactly the same in Performance mode as in Patch mode. Have the Performance Part that you want to sound like the Patch get it's EFX and Tone output assignments from the patch. I believe you will have to manually copy the chorus/reverb parameters to the Perfomance Part. (I usually set chorus/reverd to some globally acceptable values for the piece I'm working on instead of copying). Hope this helps somebody. RJ