Cheers man.
With the HD650s and TRS output, I prefer the low gain and low impedance setting. Low impedance setting is noticeably less compressed and more unleashed (especially at the low end) in a sensible way. Low gain setting when volume matched is more dense throughout the spectrum with a more substantial backbone. I also tend to prefer gain and volume settings where the volume is in the middle third of the dial’s range.
This is a quality piece of equipment - taking my time as I get to know her.