I've the rHead here at home and it is not from massdrop (got mine for 250€ in EU and it work on 220v without issues)
1) Do you need hundred review if it just sound good?
2) It is full metal except the volume control know and it does not feel cheap at all
3) It have Left+Rigth 3pin XLR and RCA input
I'd say it sound clearer than the Burson fun, actually it not that it sound better, I find it clearer and more transparent. The Burson is "rounded" sound is likeable no issue there but it is colored.
It have no issues to drive any of my headphone I don't have to push the volume to max for any of them.
(HD600, 6xx, 598, 599, 558, DT990pro, koss950, planar HE-4xx, Monoprice M565, K7xx, Creative aurvana)