Hi Mack,
I found one reference using google of someone printing using the Canon XPS drivers (
http://photography-on-the.net/forum/showthread.php?t=944235) and he says he is not having any problems. I suspect it's not really buying you anything.
Looks like you are breaking new ground. Mike always challenged people to show the difference between a properly printed image from Qimage with one printed in PS using the 16 bit plugin, and I think it's still true that nobody has demonstrated to him that there is any advantage. I'd be curious to here of any successes in this.
I would suggest trying printing in PS with the 16 plugin, and in Qimage with the XPS driver, and with the standard drive and see if there are differences.
Hope you have success.