RE: Looking for a temporary test host with a nVIDIA GPU
That would help yes
RE: 26xx v2 not supported?
I bet on a weird chip issues that confuses Xen heavily. However, Xen devs are interested to have access to this kind of "weird" hardware.
Having a serial access in the future might be interesting (to try different Xen parameters, like noreboot and so on to see what's going on)