3) Older 3 pin that uses a 4 pin PWM adapter. I read the new ones are true PWM.
4) I have the Phanteks on the CPU PWM header and I am thinking I might get better control on a 3 pin and not using the PWM adapter.
Try to connect the 3pin directly to the CPU_FAN header (no adapters), enter the bios, go into Monitoring and then to CPU_FAN, search for Q-FAN, switch it from AUTO to ADVANCED, this will change the CPU_FAN header from 4pin pwm to 3pin voltage control, re run the FanXpert2 tunning and see if it goes lower than 900rpm.
I have a 3 pin splitter so I can run both fans off one of the other fan controllers. I have not tested this yet but my idea is to run my new Noctua Redux case fans all off the CPU Fan header for true PWM control.
Well to run on PWM you need the fans to be PWM and the header to be true PWM header, a 3pin Y splitter wont work, if you connect a 3pin splitter into 4pin pwm fans they will simple run at 12V, as in PWM the voltage never varies. Now if you run PWM fans on voltage control it can work, its just simply you are running lower voltage into the motor, some say its not recommended for PWM fans as the motors are not meant to be ran lower than 12V, but then agian you get resistors on the Noctua PWM fans that lower some the voltage, so in reallity only the manufactuers knows if its acceptable to run their PWM fans undervolted, for this alone its much better to chose proper fans for each header and the way you want to control them.
I Have a swiftech Adapter to run multiple fans off the single CPU PWM Fan header. Than just run the PHanteks in 3 pin mode. That way I have control of the case fans and control of the CPU fans separate from each other. If I had true PWM cpu fans I could run all fans off the CPU PWM fan header but then I would not have individual control between case fans and cpu fans.
I think my plan will work ok? My only concern is if the PHanteks will throttle down enough when on the regular (Fake 4 pin) voltage controlled fan headers. I would like to see closer to 600rpm if they can do it. They are just to loud at the ~900 rpm they are spinning.
What i would do in your case, is to get the noctua redux but the 3pin (not the PWM) and connect them into the CHA_FAN headers, your motherboard should have 3 that matches your 3 fans you wanted to buy (2 front and 1 back).
The second solution is to grab the PWM fan splitter (can be the swiftech, although not sure what model you own) and run the PWM fan from it and the splitter connected to the CPU_FAN. Now you have the issue that you own phantek that are 3pin, you either have the option of running them on CHA_FAN headers or get some Noctua PWM for the cpu cooler also.