Ok its official! The BOSS GT-10 works with the iPad! ? ? ?
And it doesn't even appear on the compatible list!
http://iosmidi.com/devices/
I went and bought a USB connection plug for R329 (couldn't find a generic), and plugged in the GT-10's USB. I had to set the driver on the GT-10 from 'advanced' to 'standard', and monitor through the headphones on the GT-10 (can't hear anything through the iPad headphones).
I can now hear all audio played by the iPad, I can record my guitar using any of the recording programmes, and I can use the amp-sim app JamUp to effect my clean signal. This is all through the USB - no iRig or anything to do with the iPad's headphone output. Time to download some more amp sims and a DAW and the possibilities are now endless!
I'm sure this will work for a lot more other USB devices.
If it didn't work my plan was just to go back to Incredible Connection (where i bought the USB connector) and swap it for other computer stuff, so trying it out wouldn't be a waste of money.
But it seems to work, so I'm really happy right now! ?