>>I concur with Mark here. The Emu command station is pretty fly for what you're trying to do. I've been using mine for about 3 or 4 years (always loved Emu stuff...) and it's a champ. Make sure you are buying from someone with reputable feedback... I've been burned once or twice.
I'm using a Command Station with XL7, World, Proteus, and Composer ROM's. One box, simple wiring. The pads on it are pretty workable too.<<
I too am with mark & steve on this. the command station (XL7) I got this week, from a reputable ebay emu specialist, surprised the heck out of me by being more solid & feature-packed, especially in the live-edit/looping area of functionality, than I had any right to expect. the pads are pretty good too. & of course, sonically the emu proteus family is up there with the best.
being circumspect about 2nd hand stuff is fair enough, especially if you have had problems in the past, but the flip-side is that you can & will miss out on some of the esoteric hardware that never made it past the mass-production profiteering police. I don't know how long the command stations were in production for- maybe three years?, but I always wanted one (£1000 new, they were) & began lusting again after reading a few online reviews. I have a lot of emu stuff anyway. this one was about 1/3 of what they were new, & bar a little gig-rash, you'd never know it was used.
but then again, there's always the little korg. the electribe sampling unit (ES-1) would surely suit your purposes. you can easily put your own noises into it's non-volatile storage, you can record patterns realtime, grid or step. there are some rudimentary effects. the audio quality is high. the pads are.... well..... you could always get a roland spd-8 or something to go with it.... I love mine so much I bought another one.