The Firewire410 has optical output as well. Only thing is that with SPDIF it's either/or. You can't have coax and optical going at the same time...
What do you mean by "how are the pres?" Take a listen to some of the links in my first post...
As for a UA-5/FW410 comparison, I don't know of any direct comparisons. But I have run both in the field, and I do like the fw410 better. Nothing very quantitative, but just a preference.
Oh, and fyi, it's 12v DC powered, not AC. So it shouldn't be too hard to get a battery for it in the field.