Well, I dont know about the M-Audio products but I know that the PCI based Digi 001, has less latency than the USB 2.0 based M-Box. And USB 2.0 delivers 480mb per second but Firewire delivers 400mb per second. But there are other factors such as chipset. Latency is the thing you would want to minimize.
Are you speaking of the M-Audio 24/96 Audiophile card??
If so it has the same converters as the MIA card from echo, wich is an exelent PCI card.
Anyway, good luck.