I have an ASUS P6X58D Mobo, Core i7-920 (non-OC) mounted with a Noctua NH-U12P cooler in push/pull config.
I get <35 C temps in idle, very happy.
I installed Asus AI suite with Fan Xpert control, and I can control the case fan with ease.
However, using the same program for the CPU fan does not work, its always at 100%.
I have it set up with a 2 fan config push/pull using the Y adapter into the CPU_FAN 4 pin connector.
Disabled the BIOS setting under hardware monitor (Q-Fan).
Still no dice, its always at 1318 rpm.
Tried using SpeedFan, still nothing.
You have 2 4 pin fans connected to a 4 pin Y? If so your RPM signal is all messed up and it won't work.
If they are 3 pin fans and plugged into a 4 pin connector (PWM connector) you can't control them since your missing the PWM signal the fans have to have.
the latter I have proved myself but Enermax tested the Enermax Cluster fans for me with a PWM 4 pin Splitter and told me it worked .... I wound up not buying the fans because I had determined that while they are great acse fans, they don't work well against a big pile of closely packed metal fins