This is a very good point and one that should have been obvious to me. I suppose it would have been one of things that would have come to me if I'd actually been trying to get two (or more) FBV devices to work on the same computer. But yes, you're right, as long as you set up each of the devices to be sending on different channels, the ports don't matter so much if the software can distinguish between MIDI channels (which most, if not all, can). So in theory it should work. However, one thing that might trip it up would be if the Line 6 software editor can't distinguish between more than one device and so would update both devices that were connected simultaneously. Though I suppose to get around that, you would only ever open the editor while one device at a time was connected, set and assign the MIDI messages to that device, then switch to the next device and set that, then close the editor and voila!

Really wish Line 6 would develop the USB-MIDI side of these things though. They could be so good and so amazing as MIDI foot controllers and would (I think) be very popular in that area as well as the area they were initially designed for. Win-win for Line 6.