I’ve never had any problems with Quicktime, and for the most part you’re not going to run into any issues with popular software like QT. I can’t speak to your IO device, I would suggest seeing if the vendor offers a 64-bit driver on their site. Even if they don’t you can probably get it to work; WOW64 (Window’s 32-bit subsystem) is generally very good at handling 32-bit drivers/software.
The biggest problem I’ve run into so far with XP64 is recognizing external HDDs, PC or Mac formatted. For example, if you’re trying to read a Mac formatted drive you have to use a program called TransMac because the more popular (and superior) MacDrive software doesn’t run on 64-bit systems. And for PC drives, well… That’s a whole different story. It’s not impossible to get them to work, it’s just a pain sometimes.
Still, granted you’re using apps that take advantage of 64-bits like Cinema 4D or After Effects (which is still a 32-bit app but can do multiprocessing) and you’re willing to do the occasional troubleshooting, running XP64 can definitely be worth it.
(I apologize, I misspoke about the lack of codec support. This is not a 64-bit specific issue, just a Windows issue.)