I wouldn't think the quality of Roland's Studio Capture an issue... but I suppose auditioning it at a store along side the Motu would be the thing to do.
I see the Studio Capture competing directly against the Motu 896HD Hybrid. The Studio Capture has 12 pre's, the 896 has 8. The 896 more IO, as it can accept an additional 16 channels via adat, and it can interface to the computer via USB or Firewire.
Studio Capture 12 pre's - 16x10 USB
FX - bussed reverb for monitoring
Motu 896HD 8 pre's - 28x16 mix USB/Firewire
FX - bussed reverb for monitoring
Compressor (in chan,out chans)
LA style leveler (in chan,out chans)
EQ (in chan,out chans)
Price is about the same for the Roland and the Motu.
The skinny?
Roland - 4 more pre's
Motu - better mixer for live use (compression for drum kit, etc..), is expandable via adat (adat channels can be mixed within CUE mix..)
You've still got 6 balanced I/O in the MKIII, you could find pre's with output and plug into that...