How to check/change Vdimm on P5K-VM ? Do I need to?

Hello folks. So I am building a new system. I have an Asus P5K-VM, with 4x1GB Transcend axeRAM modules on there. THey are rated at 1066mhz at 5-5-5-15 @ 2.1v .
The motherboard boots with the RAM at 800mhz by default, and if I manually set it to 1066mhz, I get memory errors, reported by memtest86. I've manually set the timings of 5-5-5-15, with the same results. I think that it is possible that the RAM is not being run at 2.1v, but I'm not sure how to check that, or how to set it, if that's needed.

The BIOS does not seem to have any explicit option to set Vdimm, or to report it.

I may just have bad RAM, which would be rather bothersome, but I thought I should be vigilant and check this first.

Any help would be greatly appreciated!

Thanks,
Andrew