Okay, maybe 12 hours was too hasty. Almost as soon as I posted that I set google to only open Japanes pages, and there was a file for the 760 install kit. gambled, installed the entire suite in Japanes on my system, but this time when Windows detected the 860, it found a working driver.
Now I've copied all the .inf files into a spare dir and reinstalled the software for the 5500 and I am playing files I've dumped on my device as we speak.
Yay...