Ok I have some great news! With my newest regulator for a WiiKey Fusion or WODE. The gamecube will draw a total of 1.7A (a bit lower in game) on 7.4v. This is the lowest I can get it with everything working 100%.
Let me explain:
The GPU takes 1.8v originally. I was able to power it of 1.7v while still working correctly. Drawing 3A at 1.7v
The CPU takes 1.55v originally. I was able to power it of 1.5v while still working correctly. Drawing 2.2A at 1.5v
The 3.3v line will stay the same as putting a lower voltage in won't make any difference in amp draw. Drawing 0.8A at 3.3v
By using a PTR08060 or PTR08100 for the 1.7v line
a PTH08080 or PTH08000 for the 1.5v line
and another PTH08080 or PTH08000 for the 3.3v line
we now have the possibility to bring down the total amp draw!!!
PTR08060 and PTR08100 need 100uF caps on output and input. PTH08080 and PTH08000 only need 100uf caps on input.
Following my diagram below you will be able to see which resistors you need to get the appropriate voltage.
The other regulators on this diagram are for powering the cube of a single 3.7v battery. Amp draw is not as effecient as 7.4v so not really worth your time.
The total draw of running the cube of these 3 regulators is 1.7A (a bit lower in game). If you don't want to bother with 2 separate regulators for the CPU and GPU. You can use the PTR08060 or PTR08100 on 1.7v to power both chips. The difference in total draw is 0.2A. As running it of those 2 regulators will give you a total of 1.9A on 7.4v
It's your choice. Note that the draw of the WODE and WiiKey chips have to be added. I still need to measure those.