I'd try to get an RME UFX or the Lynx Aurora 16 or Apogee AD16x..(maybe the Symphony is also good for its expandability)
If you buy the 16 channels converters (from Apogee you'll need some DA as well, I don't know how many do you need) you are fine when you'll increase your preamps or the channels you have/want to record..
Even if they've more channels might be worthed to look at the SSL alphalink with an rme card, 24ch ad/da, sounds great and it's rather cheap for the channels involved.
If you're fine with 8 go with the UFX or anything that has 8 channels ADDA.
An 8 channel preamp like the ATI 8mx2 will get you one of the best preamps around for that kind of money in 1RU.. It also has some monitoring/mixing capabilities which you might find handy.
The ATI is a great preamp, rather clean, but with tons of balls, everything I've recorded with it came out fullbodied yet clear and not at all sterile.. If you record acoustic stuff this is what you might like..
For the 8 channels preamps in 1RU box, and for the money involved, I think this is your best bet.. Everything should fit your budget..
No more upgrades after this setup IMO, unless you need some "special" channelstrips or preamps.. like neve style stuff or so..
If you really want to upgrade the converters you will have to go with Weiss or Forssell but those are in a very different price range, and while there will be differencies, I don't know if it's worthed.. I mean changing the mic placement or the room will make a bigger difference..
Just my 0.02$,