You probably already know this, but the Amiga doesn't come with a sampler nor a midi interface. For sampling, you need an external sampler which uses the parallel port. The same goes for midi, you need an external midi interface. IIRC, you connect the sampler to the parallel port and the midi to the serial, so you can use them both simultaneously.
I happen to have a spare midi interface for Amiga if you are interested. I also have an 8-bit sampler, but I'm pretty sure it's broken. Might be fixable, though.
