You must have one of the 7950's that defaults to 1.25v. Yea you can probably just undervolt with trix but a better solution is a 7970 bios. I have the HIS IceQ 7950 I used the bios from the HIS IceQ x2 7970. I assume you probably can use any reference 7970 bios if yours is a reference 7950 otherwise you probably need to stick with the same brand if its a non-reference. Power usage is around 170w now per card, instead of 250w.
im happy with trixx. i undervolted and little overclocked cards and i made -300w in power usage. now that rig is pulling about 980w
gonna fix it some more tomorrow