I've briefly glanced through the information on the headphone amps that you cited. They definitely look premium. I hope the performance matches that.HD650 is my goto HP when I have to test an amp. Have tried it with Apex Teton, A&S Mogwai, Auris HA-2, Zana deux SE, Glen's OTL, Otomon 71A/45 based SET (which I owned till last month but sold after building my own amp). Listing only few as these amps I could see made big difference in terms of driving HD650. The so called veiled is no more there, bass sounds tight and controlled and overall you see more separation and space around various instruments.
none of these amps I would say added warmth, but there was better layering, bigger soundstage..
I'm also keen on exploring more portable, compact option. Chord Hugo looks interesting. @docharsha89 could share a brief review; along with other alternatives that come close to the amp. Woo Audio WA8 Eclipse looks promising as well. It brings the warmth of tubes in a compact device.