Hi all, I recently bought a older (2011) MBP - top of the line at the time I think - to use as a media server. Anyway. It works fine for that, but it has a really weird and annoying issue I'd like to resolve if possible. Low impedence headphones work fine from the headphone jack and an USB DAC (Dragonfly Red) but all high impedance cans have extremely distorted low end bass, even with the DFR. Like it makes the headphones rattle and crap out below a certain frequency. Plug the same headphones into other macs, perfect, plug the DFR into other macs, perfect, try and use either with this Mac, super gross low (about 60hz and below) bass. Unlistenable. So it's not the dac in the Mac, and it's fine with low impedence headphones. What could it be? Weird huh?