It's true, i'm pretty late for anwsering your question about the "not so good drums" in your (and the one I own) XP-80.
I think it's pretty simple to make your drumsounds sound better, I use a few different ways.
A. Try to make your EFX free for the drum track, now for each drumsample it's possible to modify the amount of EFX, and now the important thing try some, especially the compressor can make your sound pretty fat/thick.
B. You can also make drumsounds in patch mode, now the drumsounds are having much more possibilities, the biggest advantage is now haviing the booster for your drumsounds, and that makes a big diggerence! When your not sattisfied at first glance just keep trying adjusting some filter values, pitch values (detune) and envelope values.
C. Try layering the drumsounds, but when you do this you have to experiment with the filters (also the BPF and HPF besides the LPF)
I hope you can take you're advantage with these 3 points, please let me now if it was for any help for you.
I'm a newbee, so excuse me if these are common known facts, or maybe they are but didn.t you think of these possibilities.
Succes!
P.S. Let me know if you got some other interesting point for improving the drum sounds.
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Amsterdam (NL)