Here's a convoluted tech question for you USB/Midi experts:

I'm trying to determine if it's possible to use a Yamaha YPG625 keyboard as a controller with a Yamaha PSR E403. Unfortunately, Yamaha doesn't supply MIDI ports on these two units, only USB to Host ports. I know I could make it work if I plug the two into a computer with 2 USB ports (or use a USB hub), but I'd like to avoid having to complicate the setup with a computer. Ideally, I'd like to be able to simply plug the two together using a USB B-to-B cable, but I don't think that would work as the USB interface is not peer-to-peer, correct?

Any other ideas? Does anyone make a special USB/MIDI box that would allow this kind of connection without requiring a computer?

Thanks for any ideas!