I've only seen the ones that work, and man are they something. I think these are still reletively rare occurrances ,percentage wise, (makes you feel better already Huh?? Yeah, thought so...), but they get talked about alot.
I went ahead and bought AB10K's for my tank. this was before I read about how great the XM's were (PAR wise), and then discovered my ballasts have trouble lighting the XDE's...so I wasnt able to use them anyway...
I have the lights on over the tank right now, and I'm very happy with how white the light looks. I'm sure that once the bulbs burn in, they'll yellow a bit, but have you thought of using the AB10K's?
Nick