Now, you have successfully flashed to stock original BIOS, there are only Asus Smart Doctor, Saphire Trixx & Gigabyte OC Guru.
I will take a look at the BIOS in awhile and see if I could edit the voltage for you.
Sorry, the card doesn't have software voltage control. Meaning, the only way to raise the voltage is by voltage hard modding, if you want to go there.
The above softwares will not do you any good and won't be able to tweak volatge simply because it is not there in the first place.
So forget about voltage, just be happy with the stock voltage with stable highest clocks.