Sure, you could probably do everything in the S910. But, given that the OP has already admitted to a dedicated USB-audio converter, is it the easiest OR the quickest..?

TBH, given the FAR better options for punching in and out, 'comping' a great take from several average ones, and the far better vocal pitch correction, compression EQ and reverb that computers offer, I'd say that doing your BV's in the computer is leaps and bounds ahead of doing it in the arranger.

I don't think the OP is looking for an 'arranger only' solution. Just whatever is easiest and more efficient for a given output quality. The S910 is a nice piece of kit... but it doesn't adequately substitute for a computer, DAW and audio interface, IMHO.