You would not use PWM for audio electronics obviously and I have not seen any coupling of the PWM frequency on circuits running at 100% duty cycle. More switching does mean more heat on the FETs because the gate spends more time out of saturation on the way up and down, but if you watch the video, you'd see that I am using FETs that warm up just a few degrees at 15A (<1 degree in the 3A range) which is the max current per circuit.
Also, because the PWM generator only outputs a single frequency if you turn it up on one circuit they turn up on all. This is likely to confuse some who do not understand the difference between "duty cycle" percent of time the circuit is on, vs "frequency" which is the speed at which it turns on and off. There is also the issue that the gate resistors on the FETs ought to be tuned to the frequency so that there is no ringing but the spend as much time as possible in saturation. A resistor that is good for 60Hz will be way too big for 60,000Hz.
I am not opposed to allowing a few settings that should work for most users (40,80,120,160) perhaps. I don't think anyone is going to see 160Hz.