Sigh. I'm about to pull out these fans and just go back to stock. This is driving me nuts .
After spending some time in this thread, I think I understand what's going on.
Yeah, at ~3v, many fans won't even start, so your Sunons situation is understandable. I'm pretty sure they manufacturer messed up somewhere and they meant to do 12/7/5v originally. Having 3.9v and 2.7v makes no sense to me.
So, from my understanding, here's what you're looking to get:
Ch1: 4*.4a=1.6a, 1.6a*12v=19.2w ~22w
Ch2: 2*.53a=1.06a, 1.06a*12v=12.72w ~14w
Ch3: 3*.45a=1.35a, 1.35a*12v=16.2w ~18w
I did some curiosity testing with my Noctua NF-P12 fans. It is rated for 12V, 1.08W, .09A. So I busted out my bro's Tenma Laboratory DC PSU, and at:
NOTE: at 12V, the starting load was up to .217A
Seems like with lower volts, you get lower Amps as well. Now we have to figure out what introducing resistors here does.
Let's try Noctua's resistor thingies:
Low Noise (1100rpm): 12v, .06A (same as 9V)
Ultra-low Noise (900RPM): 12V, .052A (same as ~7.5V)
Conclusion: resistors don't seem to significantly increase wattage.
V= R x I
It seems like you fried your old resistors because the load was too high. They were no designed to handle more than 1 fan per channel, probably. You'll need to get more proper and much more powerful resistors (or get a few and solder them in parallel)
Ok, I'll have to stop here. Gotta go for the weekend. I'll be back Sunday to finish the calculations. Also, I'll ask my brother who know way more about this than I do on his advice.
Hope this helps.