Thank you! I love sharing stories with my gear, I can't lie :D

The HD6X0 Series are just fantastic, I had a HD600 for a while before I traded to my beloved Grado RS2e and part of me to this day wonders if I made the right call there because as much as I love the Grado, the HD600 was something speical. I will say, personally, I think DAC / Amps are all snake oil past a certain point. So, look into it a little more before you pull the trigger.

I currently use a BTR5 for mobile use and a $30 Behringer UMC22 for my digital desktop side. I had a Topping A30 II / L30 II DAC / Amp stack and I honestly... after dB matching, I couldn't hear a difference between that and my UMC22 with my HD800S which people claim is a very source dependant headphone. I gave it all the benefit of the doubt too, ran it side by side through Roon. It was all the same. The most expensive amp I've tested is the Naim Uniti Atom and, again, it sounds exactly the same, but it does have a cool screen and dial on the top.

Something to consider, having a good source is good of course, but anything audiophile grade will all just sound the same.