Keep in mind, ratdog, that a preamp or receiver can serve as an external DAC. For the most part, I think you'd be OK with going that path, rather than a fully external DAC. For example, the Benchmark DAC-1 is a well-respected outboard DAC, but it'll cost you $1k by itself, and you'll still need amplification. It shouldn't be too hard to find an integrated amp or receiver under $1k that will do both the DAC stage as well as amplification.
An integrated amp, receiver, or DAC that has a firewire interface will be hard to come by. It's possible that they exist, of course, but I'm not familiar with any. In general, I'd expect to go optical or coax digital from the soundcard to the integrated amp/receiver.
As to recording possibilities, many can accept a line-level input. If you need a high degree of fidelity, you may have to do some research. If you just want to be able to record a line-level stereo source for general purposes, most can do that with an analog input (and some with a digital input).
