I don't worry too much about audio quality of MP3s. I rip everything I get new as 160Kbps MP3s, but I don't play MP3s when I want to sit down and pay careful attention to listening to music. I have LPs for that.

For just background music when I'm working or whatever, I find the quality of MP3s to almost always be good enough. Of course, it's a matter of taste.

I wonder about the vacuum tube USB amp... is the DAC really good and clean? It'd be kinda silly to feed a harsh, nasty DAC output full of HF garbage into a fancy tube stage...