Multi sampled synths are a total menace to make and besides lots of people use different samplers these days, you are not going to be able to deal with that kind of variation without tearing your hair out.
Why are they a menace. Play or get a midi file to play each note (or 3) over a few octaves. Not hard..???
I'm not meaning sampler patches. But I see so many sample packs with synth hits at about 3 notes (or just single hits) which are kinda useless...