all good except that you will find many more USB DACs then FW DACs
I was under the impression the poster was asking about storage devices to store the music library on, and not about DACs.
If you are asking about the DAC interface I'd be looking at asynchronous USB DACs. Firewire DACs are few and far between, partially because software needs to be written for each operating system and update thereof in order to use the DAC. There are other advantages to the USB interface from the functional standpoint. There's another thread on this subject
here which gets into the interface debate where the DACs are concerned, but you'll have to sift through quite a few responses.
From that thread, definitely check out
these interviews for some interesting viewpoints on the current state of computer audio.