Ok lets break this down, and tear down some rumors.
I have an asr 10 + asr x (black) with scsi in both.
So lets get right to it, first asr 10 has more editing features in some ways and is more geared as a keyboard sampler. The machine has a tape recorder function as well (2 track recorder basically). The sequencer in both is good, lets say that a again the sequencer is good. Now the asr x does not play all asr 10 sounds perfectly sometimes there will be differences although I wouldn't worry about it.
ASR-10:
- Keyboard sampler driven, heavy editing features, 2 track recorder and better navigation ( i think) arrow keys over knobs. There is also a few more things probably in the asr10 OS thats not in the asr x and vice versa.
- As a general rule ASR 10 os is more stable, but I will explain this later.
- 16 mb is max ram, still quite a bit and surely enough for my needs. Wu tang made there album on an EPS, I think the original maybe not even the full 2 MB heh and it turned out pretty good.
- I know the ASR 10 os better and its easier to navigate *for* me
- Also if you need keys and want an asr machine its a one package deal.
Now for the ASR X / Pro
- The machine has built in sounds, it has a small MR synth built in (really good synth) and you can add quite a bit more sounds with an expansion card. There is 3 of them but can only use 1 at a time. (Dance, World, Perfect Piano). The machine stock only has 2 MB of sample data compared to the stock 14 MB of stock sample data in the actual mr/zr. With that being said its pretty much a free added bonus and you do get quite a bit of sounds and alot of hip hop geared stuff.
- You can get much more sample ram then with the asr 10, 16 mb vs up to 32 mb with the black model and i *think* 66 or maybe 88 mb with the red pro model. Anyways you get quite a bit more sample time, but remember this does not effect me at all. I don't sample a large amount of stuff, my asr can do 3 minutes at 44.1, good enough for me for sure, but hey its nice to be able to have more I guess.
- You can midi a keyboard in there and then have keys which I would highly recommend, nothing wrong with the pads but keys are my thing,
- I think the red model asr can read wavs now, this is a pretty big plus, maybe the black model with the last os (maybe) not sure about that but I know the red model can.
There are my small list of advantages now for some rumors.
- The ASR-X sequencer does not skip or mess up if you have the latest OS for it, 2.67 is an absolute must for a black asr, if you see one that has an earlier be prepared to spent 20 or 30 bucks getting it upgraded. You have to buy some rom chips with the new os on it. For this simple reason the red asr x pro is a safer bet since it allows ou to put whatever os you want on it, I think it goes up to 3.01 or something but its still pretty much the same as 2.67 nothing major was added if i remember correctly. Now the sequencer can skip if your browsing through stuff or loading other banks etc haven't had it happen ( have not used it in a while) but I believe it could happen, but this does not effect your music making at all. The skipping from the black model had something to do with the timing correction that you can apply, they fixed it though in 2.67 once again so don't worry about it if you have black one with this os
Well just one big point I guess
Anyways the asr 10 and the asr x are very similar, with one you get a synth with built in sounds, with the 10 you still get a synth ( you can record yourself whistling and put it on there and have a full synth whistle, although the professionally recorded ones might sound better

but you don't get built in sounds but you can load them from many disc by ensoniq and many other companies.
asr10 - scsi is a must unless you get it super cheap and dont mind the floppies, it will be a pain but if its free them heh.
asrx- black is fine as long as you update or already has 2.67 os, also black with SCSI or you will be in the floppy boat. Red has SCSI as a standard so thats another + for the red machine in a way.
You have many other options as well though if you want the ASR sound, you can get the rack versions you can get the dp-4 or whatever its called effects rack but its all up to you your work flow and how you want to do things.
Happy ASR'ing and hope I helped.