Well, are you talking about an external firewire hard drive as well as a PCI audio card? If so than the answer would be no as you are taxing the PCI bus even more at that point. Firewire is popular due to the fact that you can use it as a back up device or for a laptop as a secondary drive.
Recording through firewire isn't much of an option as far as ASIO goes but there is Yamaha's mLan which is an ASIO firewire protocol. Yamaha just put out the beta mLan ASIO for PC and I tested it out this past weekend with amazing results! Very low latency and great operation..I still need to do more testing but it's pretty rocking so far!
Opus :D

There are many reasons firewire is so hot. First cuz it's FAST! Second cuz so many things connect with it. Digital camcorders, storage devices, computers, even consumer electronics (they aint cheap). My preamp on my home theater has firewire (Upgrade) ports on it, so your question made me wonder... "what the hell are those things for?" I'm not sure of all it's future capabilities but check this shit out. crestron . It's pretty wild.
I mean I used to (I thought) know it all about audio, then came pro audio (totally different as we all know), NOW high end audio stuff these days is pretty wild! :)

AES/EBU is a standard digital format. Digital stereo signal in fact. So one XLR connector carries a stereo signal with an embedded clock to maintain digital integrity. AES is actually the preferred connection as it is a secure connection, low jitter and a very reliable source.
So if you had a device with AES on it you can take the signal from or to the Pre.
As far as the firewire stuff you mentioned...exactly!
I have my whole system networked via firewire and I can put a DV cam on the hub and all systems can use it at once!! how cool is that! lol
Opus

Exactly. But what kind of device? I'm not familiar with any that have a single digital output like that. :confused:

Devices like CD Recorders, DAT Players, Audio Interfaces, A/D or D/A converters...some PCI Audio cards come with AES on them...
Opus :D

Hmmm. I want one.