Sony M10 (and the bigger D50) have excellent ADC (analog in). In fact, I would say *better* than UA5. So, you're best setup is: mics > (optional pre) > Sony. If mics run on battery, no need for a pre at all. If you need gain, or to drive phantom powered mics, the MP2 is an excellent preamp.
The only reason I would tinker with an Edirol UA5 or similar is as a USB input device. Everything else can be done better (and simpler) with a flash recorder!
Richard