I've got a 6400 ultra with an rfx card but apparently the power supply is too weak to feed both (+an internal ide hd). I sent the sampler to Germany for repair in Septembar and they still haven't received a replacement power supply from EMU.
I even called EMU-sales in both Ireland and Netherlands to see what's going on but as things stand t doesn't look good. The answer from Netherlands (which is apparantly where EMU's EU-HQ) was that they haven't been getting any for a while. I checked EMU's website too and they don't even mention their hardware samplers there as far as I can see.
Anyhow if anyone knows of an online shop or a service center which has one please do let me know. I'm quite desperate at the moment as it doesn't look like they can get one of those and I really don't want to loose the rfx just because of the power supply.