The only downside I see to the Duet is that it doesn't offer Digital IO, which means you can't add a better AD converter later if you wanted to. You probably won't care though since it is an Apogee and it already has a pretty great AD converter built in. Apogee is a higher end pro audio product and is known for it's sound quality above all. I think it's the no brainer choice for what you want. There is a PreSonus fire box that could be had for 300 bucks, but I would guess it won't sound nearly as good. If you wanted to spend more (probably not) then check out the Metric Halo ULN 2.
I will be real interested to see how this works. I may be following your lead if this works easy and sounds great. My setup sounds great for sure but is not the most convenient.
That Apogee and a laptop is portable as well. You can buy it from Sweetwater sound, they are pretty good to deal with.