I've been looking at getting a second fan identical to the one included in the Scythe Mugen 2 package. The review on this site says it's SY1225SL12M-P, however when you visit the the Scythe website the only PWM 120mm fan is a DFS122512L-PWM. When I visit any retailer website selling the SY1225SL12M-P, they always indicate that it's 3 pins with a 4 pin adapter.

Is the DFS122512L-PWM the only option if I want to split the power and RPM signal across two fans?

I'm uncertain exactly what you need.

Here are the four Scythe PWM fans:
http://www.performance-pcs.com/catalog/ ... lter_id=73

That is all you have to choose from.

This one is especially interesting if you want to use 2 fans to extract the most out the Mugen, but keep it quiet.

*** NEW *** Scythe SY1225SL12HPVC Slip Stream 120 PWM Adjustable Fan
http://www.performance-pcs.com/catalog/ ... s_id=27544

Features:

PWM Adjustable:
By adjusting the controller on PCI Bracket, the band of PWM range can be set as below.
This switch can be attached into any empty PCI Slot.
Small Center Hub & Wide Blade Type:
By reducing the dimension of the center hub and enlarging the blade surface area, high airflow is generated at a low RPM.
In Order to take advantage of PWM function, please use the motherboard with PWM features build-in.
PWM function will not work if the fan is connected via 4 Pin peripheral connector or connected to 3-Pin fan port. In this case, the fan will spin at the maximum speed.
Connection to any third arty market fan controller with 3-Pin port, PWM function will not work but fan speed can be adjusted by the fan controller.
Specifications:

Maximum Band 740 (±25%) ~ 1900 (±10%) 9.8 ~ 37.0 dB 37.15 ~ 110.31 FM
Minimum Band 470 (±30%) ~ 1340 (±10%) 7.05 ~ 27.3 dB 23.0 ~ 76

The Mugen 2 fan has a label saying SY1225SL12LM-P which is a PWM fan (see for example http://www.frozencpu.com/products/10026/fan-639/Scythe_Slip_Stream_120mm_x_25mm_PWM_Fan_-_SY1225SL12LM-P.html) and this is not the same as the SY1225SL12M-P.

Scythe possibly confuse things by shipping a 3 pin fan to 4 pin molex adapter - the 4 Pin peripheral connector - with their PWM fans. This allows the option of deploying the fan as a conventional (in this case 1200 rpm) fan as it bypasses the PWM function.

I have split the power and RPM signal across two fans using a PWM splitter cable. It works fine if both fans are the same spec. Some of those have tried this with two fans of different specs have reported problems such as unstable speeds.

For PWM fan setups to work as quietly as possible it is necessary to set the BIOS options. With Asus motherboards I turn Q-Fan on and set it to Silent mode.

Thanks a lot lodestar and ces, I didn't know the LM vs. M and the store link you gave me was the best price!

I just received the fan and it's making a slight squeaking noise at intervals i.e. like ticking but squeaks x amount of times per minute.

That's disconcerting, I just ordered a SY1225SL12LM-P. It should be on my doorstep today, though I probably won't have a chance to install it for a few days.

Does it also tick/squeak if you DON'T power it via PWM?

Actually I just checked today and it's gone. I guess it had to work itself in, remove a bit of something or who knows what. I currently have my CPU 3 pin split to two PWM fans.

??? Do you mean your MB has a 3-pin CPU fan header, and you're using it to power two 4-pin PWM fans?

Nope, just accidentally said 3 pin instead of 4 pin