Got it. Sounds like you are a bit of an audio person. Behringer gear is a pretty good balance of quality and price point, and I use their DCX2496 and 3 A500 amps for my tri-amped stereo listening setup.
Since you have the option to run a digital signal all the way out of the PC to a good DAC, definitely do that. No motherboard is going to have an analog section that comes anywhere close to "prosumer" grade gear like the stuff you listed. Your Maudio PCI card is also going to be worlds better than any onboard audio implementation.
What do audio purists do? Well, it depends. Many times, "audio purists" end up spending money on snake oil and vaporware because the marketing for those products gets to them. It comes down to basic psychology...if someone spent a bunch of money on some audio thingy, their system most likely WILL sound better to their ears simply because they know that they spent the effort and money (psychoacoustics is a big thing). When someone expects a difference in something that they are using their ears to measure, they almost always will find that difference even if it is not real.
I bet that "purists" would say that a PWM fan is bad because, you know, square waves and EMI and other technical terms that sound bad for audio. In reality, it makes NO difference if the fan is controlled with a PWM signal or not. PC fans have been of the brushless DC type for a very long time, and the actual method by which they are commutated (controlled and actuated) is essentially PWM, or at the very least square pulses through the winding phases! The speed control signal, which is what I assume you are asking about, has basically zero current, so EMI will be minimal from that. The fan motor itself is the high current device, and its speed it controlled via PWM or square wave through the windings, so the bulk of your EMI is and has always been from the fan motor. In effect, it does not matter if the can speed is PWM-controlled. Basically, you want to run the fan at the lowest speed possible to maintain your thermal targets since a slower fan is (almost always) a quieter fan. Since PWM control lets you control fan speed, I would say that it is fine to use!