lucid, I am very interested in these pc based systems that you are referring to that are "equal or even superior to ProTools".
Last I checked, real studios still use PT because it offers the best computer based recording system on the market! Period!!! Do you think that a studio that needs to do high end work would spend the $30,000 on a PT system when a $2000 PC system would be "equal or even superous to ProTools"? Dude, I will bust your chops here as gently as I know how. That is totally, 100% misinformed BS!!! Only somebody who hasn't ever worked on a PT system could possibly try to compare PT with PC bases software with little dinky 10 I/O soundcards and what not.
Currently, there are only a FEW platforms that are even remotely LIKE ProTools! Sadie, Sonic Solutions, and SoundScape. I suppose you could throw some of the more minor systems in like Paris, and Orban, but they are minor players in the "stand alone Harddisk/Computer" system. All have their OWN DSP and use hard drives that are on their box. The computer they interface with is simply that, the interface. The computer itself does nothing but command the proprietary box what to do. VERY different than PC systems that people around here are using. I can assure you that the QUALITY of the DSP in PC software currently isn't anything CLOSE to what the proprietary stand alone systems are!!! PT's DSP is at like 48 bit internal, and it can do that over as many tracks as you have hardware to run! No having to upgrade RAM, then the CPU, then trying all sorts of silly software/hardware tweeks! PT just plain WORKS! Yeah, you still need to get the computer interfacing with it right, but that is just the GUI, the actual ability for high track counts, open software capatibility, and quality of DSP in a PT system blows away just about anything out there. Yup, I think Sonic Solutions has a bit of an edge in sound quality, but SS is VERY expensive compared to ProTools. I have heard some work done on a Sadie system, and it is indeed right in there with PT!
If you are serious about recording, and need LOT'S of DSP and TRACKS and a system that is stable, you wind up paying BIG BUCKS for one of the systems above. I can assure you though that they are worth every penny when compared to some kind of cheesy PC solution!
As far as other soundcards that will interface with ProTools Le or PT Free, I am not too sure what they currently support. If you have a legal version, you should try their tech support for what might be a good card to use.
Good luck.
Ed