I'll try building eDrummer for the Rpi
The drum map I supplied with it uses nearly the full set of velocity sensitive samples from the salamander kit. This is a
set. That's what my beta tester wanted -- the highest quality and largest selection of velocity levels, suitable not for running on a COM like the raspberry, but a desktop PC. Besides the fact that your setup doesn't need a set of velocity-sensitive samples at all, even if your pads were vel sens, I'd still go with a slightly trimmed down sample set for a constrained device like the pi. (Phil is really picky about vel levels, more-so than most users would be).
The reason I asked if you wanted to work with me on this isn't
because I don't think you, entirely on your own, can compile/test an edrummer setup that isn't tuned for your system. It's because, with a little info about your setup, I could supply you with that tuned setup right at the start. Also, if you like the results, I could implement additional features tuned to your setup, such as loading different kits when you press a pad combo.
Anyway, this is just FYI. I do realize there are folks who simply prefer doing it on their own. So, moving on...
Are you using hydrogen to load a kit that you
play via pads? Or is hydrogen itself playing the (sequenced) beats? If the former, then eDrummer already is designed for that. Phil was having the same problems as you. He was trying various linux programs for live drum triggering and he just couldn't get the latency low enough. (But note Phil is very fussy. He actually has a measuring setup he uses to test latency down to microseconds. He's obsessive... and I love that. He went from 9 ms latency with a jack app down to 2 ms latency with edrummer playing the same kit on the same hardware. He's happy). If you're interested let me know, and I can work with you to get a setup tuned to your system. But I don't have a pii, so you either need to compile source on your pii, or have someone willing to do it (maybe auto).
edrummer is based on my gig software of a drumbox, which plays various drum patterns programmed into it. I've gigged with it about 4x a week for the past 4 years. (My Windows version 3 years -- Linux version 1). If you use hydrogen to play sequenced beats, then you may want to become the first beta tester for "eRhythm", a varient on drumbox that loads a MIDI file of a drumbeat and plays it back on a sampled kit like eDrummer. I anticipate something available within a week from someone serious about beta testing.
Let me know if you're interested.