What would it take for a volt mod? Soldering around on every single step down converter?
Yes, you need to change R9 resistor value in step-down converter, according to datasheet on TPS40193
the formula is
R9 = ( Vfb * R10 ) / ( Vout - Vfb ) , where Vfb is constant = 0.591v , R10 = 10.5k
for example, calculation for Vout = 1.2 give
R9 = ( 0.591 * 10500 ) / ( 1.2 - 0.591 ) = 6205.5 / 0.609 = 10189 , 10k resistor
in datasheet maximum Vout = 1.32
R9 = ( 0.591 * 10500 ) / ( 1.32 - 0.591 ) = 6205.5 / 0.729 = 8512 , 8.5k resistor
To make ~ 8.5k resistor from 10k you need to add in parellel 60k resistor, but i would advice you try to increase voltage in a little steps like 0.01v before you reach 1.32v and look at hw error rate.
Sorry but i cant point you now where is that resistor located, i just look at hash_unit schematics.
How far (in % of HW errors) can I go up with the frequency without risking of damaging something?
I think hw error rate 2-3% is the highest that you want to see, more than that is a waste of energy.
You can damage the chips by increasing voltage to more than 1.32v - be careful.