I would stray far and fast from this idea. Not because of any issues I see with the line outs themselves, but because the signal path with undergo many unnecessary A/D conversions.
The UA5 doesn't have analog passthrough, which means your signal would go:
Analog (mics)>digital like if you ran an iRiver or JB3 behind it
Then
Digital>analog on the line outs
Then
Analog>digital in the R1.
Not good. If you want to go 24 bit with the UA5, look at a laptop, I'd say.