I've sent another email to Epox Support and they have already answered:
Hi,
I'm coming here again because since I've taken part of Anandtech's forum, I've read some posts of people complaining about the undervolt issue. One of the guys there has received the following answers:
Dear Sir
...
2.About the voltage too low ,because on board sensor check point have difference,but voltage support is normal.
Dear Sir
The board support power was correct ,the sensor check was close but not at the point,so the voltage's numerical have some difference.
Well, in fact, USDM and the BIOS give me bad information on Vcore or not? I really need to know this because of the overclock... do they read it correctly or not? Currently, as my A64 3000+, 1.8Ghz, is overclocked to 2.2Ghz (A64 3500+), I've set the vcore to +0.075 (I have the 9NDA3+ rev. 2) and now is pretty stable... Before that, my Kingston Hyper X UL kit (2-2-2-5-1T, 2.7v), in stock mode (1.8Ghz, vcore OFF) was stable, but overclocking the processor made me have some memory crashes when tested with memtest86. v.1.51... increasing the vcore with +0.05 seemed to have solved the problem, but, sometimes, when I rebooted the system, I've experienced freezings... now, I've set vcore, as I said, to +0.075; USDM and BIOS read it as 1.39-1.45 (is that reading correct?) and the system is rock solid. Memory is working in stock frequency, 200Mhz - DDR400.
I look forward to hearing from you.
Best regards,
Alexandre Maciel
The answer:
Dear Sir
The board voltage in bios monitor was for check ,but it have range about the 5% miss ,because the check point have difference at sensor position .The power support with board for processor ,chipset and devices is normal,you can do adjust voltage step by step for system overclocking,but we are not suggest user run overclock too more,because overclock was so easy let system crashes and devices life be short.
So, this way I think it's completely clarified... in fact neither the BIOS nor USDM give us correct reading on vcore...
However, now I have a doubt: am I seriously risking my processor by setting vcore to +0.075 in the Bios? I've got stability by that... I don't know why, but after installing my new memory kit I've had to increase vcore. Even setting it to +0.05v gave me some memory problems. Before that, with my old sticks, I had complete stability in OC even with vcore set to OFF. I wonder if it has to do with cpu memory controller?