Hi,
I'm setting up a little home studio and one thing I want to add is some retro goodness.
I'm planning to add an Amiga into the mix (sorry) for a couple of sound types:
Why "sorry"

1) Hardware bit crusher
Get an Amiga sampler and put it into monitor mode, it'll play whatever comes in through the audio outs. It'll be "bit crushed" down to 8 bits and a lower sampling frequency in the process. Some sampling software does real time FX so it can make it even messier.
2) A grungy sampler
Use Paula in 8 mode to play back 4 channels of audio samples. Lower the sampling frequency for extra grunge.
It's the second one I'm asking about. Modern Amiga audio software uses mixing to give you more than 4 channels. What I want is the old style 4 channels with no mixing. It will also need MIDI to trigger samples.
Does any newer(ish) software still do this or do I need to go digging for something old.
For MIDI triggering the first thing that come to my mind is OctaMED SS, but I'm sure there are others that can do the job (but if I remember well e.g. Bars'N'Pipes and Music X don't support audio samples).
Sorry: I didn't play that much MIDI stuff with my Amigas in the past (but I'll do in the near future

...same reasons as yours).
For converting source audio in real time to 8 bit you can use the classic AudioMaster in monitor mode, but I think also many other sample editors of that time that support parallel digitizers.
If I remember well, AudioMaster IV does also some real time processing effects to play with...
BY and have fun!