Simple audio-mid interface - firewire or usb?

[EJ2]

Greetings all,
I've just purchased two new computers for my studio - a 24 inch iMac core 2 duo and a HP Quad 9600. I still have a PC Hyper Threading XP machine with Sound Blaster Audigy Platinum Xs for my audio-midi interface. It's loaded with all of my music utilities and files, so I'll be toggling between the two PCs with a KMV switch.

However, I'm in the throws of searching for a simple audio-midi interface for the MAC. I don't require a ton of audio inputs because I already have an old Roland M240 24 channel line mixer connecting all of my synths and drum machines. In addition to that, I still use my MX-8 6 in 8 out midi patch bay. I could be convinced to use a multi-port USB or firewire interface. In addition to hardware synths, I have a ton of VSTi and sample libraries that I wish to integrate. I'll be using the OASYS 76 and Kawai M8000 as my main controllers. Of course, the MX-8 allows me to reroute the midi controller signal from my other keyboards.

So, what seems to be a better choice - usb or firewire? Any recommendations for a simple, cost effective interface?
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Cheers,
Eric