Here's the scoop-
Yes, it's all about the sample and bitrate of a machine that makes it "fat" or not- I own a MPC 60, have owned both EPS and EPS classic, and have had a lot of friends with the Asr 10 and X. Let me give you my observations:
As far as warmth from the drums, the MPC beats them all hands down- 12 bit @ 40khz ain't the holy grail of gritty, but it has a lot more punch than all the Ensoniq stuff.
Please stay away from the EPS series- save your money and get the ASR 10. The X has built in sounds, but the DA converters make everything sound "plastic" (for lack of better word) and I couldn't make a damn thing sound raw coming off it. The EPS has a serious flaw in the design, There's simply not enough headroom built into the playback engine to make your sounds warm- and also, to even fake it, you have to copy the waveform to layers, but everytime you do, you rob precious polyphony- and those boards maybe have 16-20 voices. (Meaning sustaining sounds will get cut off, especially when layered against a fast bass synth sound.) The synth capabilities on both boards are feable at best, and then you still have to find these archaic memory expansion cards AND the super-illusive output expander to even make the EPS series worth looking at.
If you really want grimey, do a little thinking- you're not going to get a lofi sound by using your 24bit converters on your soundcard reading a CD player... Maybe you can dirty up your sound BEFORE it hits your clean sampler...