Hi kirk. If I understand you correctly (unclear a little, but I think you want to control your GPU cooling fans yourself?), personally I'd be a little bit hesitant to do what you want to do. If you had a custom water loop with a GPU water block your system could monitor the GPU entering and leaving water temperatures and control off of that. But since you have an AIO cooler with those graphics cards, those fans want to control based off the GPU temp and are designed with their own closed loop feedback. Unless you monitor that temp closely (and are sure of what you are getting), then you could potentially burn up the GPU by not ramping the fans up enough in your final profile. Also, GPU temps tend to rise and fall pretty quickly so you'd still need an aggressive fan curve.
I am guessing you want to do that to have more control over reducing fan noise? I can't think of any other reasons to do so. If this isn't what you are trying to achieve please re-post and explain a little clearer.
I think (?) the only way for you to achieve what you are trying to do is to use your motherboard's T-sensor1 header and run a temperature probe to your #1slot GPU and control the fans off of that in your system software (e.g. AI Suite Fan Expert). I suppose you could place that probe directly on the GPU if you opened it up (not recommended IMO) or just surface-mount the probe on top the card near its location. You would need a period of testing and balancing to determine what temperatures off the probe match the temps you suspect at the GPU and adjust the fan profile based upon that.
As a side note, I am doing exactly that, sending a temp probe to my #1 GPU surface to monitor temp there and control fan speeds. But it isn't a critical control loop like you're messing with, mine is just an override to ramp up my case fans if things are heating up a bit more than the CPU. My GPU isn't going to burn up on me, it's internal fans take care of it.
😉
Davemon50