I'm a tad confused but probably because I'm not too familiar with USB2; I do believe that the plug/socket geometry is the same as in original USB - no? And a Firewire plug won't fit into a USB socket; not without a scrunch.
SBP2 = Serial Bus Protocol 2 and is the standard Firewire protocol I see when I plug in my La Cie external HDD. Nothing to do with a sound card. (Maybe you were thinking of Sound Blaster).
So, I lost it when you said that you have to changeover the USB plug frequently to keep the HDD running. Is this a Firewire device or a USB device?
Please could you tell us a bit more about the exact hardware set up?