I think you can have fixed velocity by going into MIDI 1-7 and changing TrgVel=127.
Yeah, page 64 of the manual.
By default it’s variable. You can set the level ( 1-127) you want it played back no matter how hard you hit the pad.
I love my DTX, it’s a great controller and tone generator. It has 64mb of memory, which is really designed for one shots. If I planned on using it as a loop machine, I would take the time to program the loops into the DTX using MIDI and it’s tone generator. This would let you get much more time out of the DTX than using 64mb of wav memory.