Naw, looks like I'm out of luck. I found some more stuff by googling. It seems that the only ExpressCard-to-USB adapters are just a couple of wires connecting the pins. The idea is that some expresscards are, at their heart, just USB devices in the expresscard form factor. Broadband modems are a common version of this. Such an adapter will only work with those kinds of cards.

So unless I can find a 1394 adapter which does the complicated bit of actual USB translation, I'm out of luck. My googling tells me that no such thing exists.

So the Sony Flip is not something I'm going to ever buy since it doesn't have firewire or expresscard.

Might just choose to get a Mac for the studio still (would need the thunderbolt to firewire connector), and keep searching for a lighter weight version of the music tablet as a separate device.