I'm looking to replace a M-Audio 2496 PCI with either a USB or FW interface. The hardware is marginally fast enough as it is, so I'm concerned that actually switching may push things over the edge. In particular, I've tried using a Line6 PODxt as a USB output interface, but periodically (particularly when playing video or flash) I get loud bursts of noise, that I interpret as being the computer failing to keep up with feeding it. Maybe my interpretation is wrong. Might FW be more CPU efficient, or do I really just need another PCI card?