Extremely noobish audio interface question

[MDV]

I'm using a PCI card with breakout box at the moment for all my PC sound: which pretty much means all my sound.

However, the 2 xlr inputs on my emu 1616M are starting to feel a bit cramped and I'm thinking about upgrading to either a firestudio or RME fireface 800.

My question is can I use one of these firewire interfaces as a permanent soundcard for my PC? Cos I listen to all my music via the EMU one way or another (upsmapled MP3s in winamp and CD player via ADAT into monitors and an amp and hi-fi speakers), and this would have to replace that setup.

Could I enable the on-board soundcard (not a half bad card due to overkill motherboard) and use them both? Would I have to disable said built in sound card to use the fireface/studio?

Could I run a fireface/studio and the EMU PCI card at the same time (i.e. have them both installed, and use them seperately)

And to anyone that can answer this: is it worth upgrading in the first place in terms of AD/DAs, preamps and latency from teh emu to the RME or presonus? The EMU does a remarkably good job in these areas for its price point, I'm worried that this gear wont be much better! And anyone who has an opinion which is better out of the two, please speak up!

[JJretroTONEGOD]

RME are seriously the best! presonus are still good, but RME are well ahead of the game. I regularly go on production forums, and I hear producers talking about the RME AD/DA converters to be the best that money can buy, some of these guys are mastering engineers! even they say RME are the very best, you'll notice a massive improvement in quality and headroom, apparently RME are unbeatable, they are used in the very best studios.