It will have no trouble driving the Focal Clear MG or the Sennheiser. A 300 Ohm impedance is normally an easy load to drive. As impedance goes down (I have DCA Stealth 23 Ohm headphones) more current is needed and some amps can’t really do that for loud passages. The sensitivity of the headphones is also a factor, but the Clear MG and the HD 800 are fine in that regard as well. I have the Atom HE and the ‘regular’ Atom. The difference in headphone capability is quite evident. The regular Atom really needs easy to drive headphones, but the HE can drive just about anything.
I’m using Focal Clear Mg and Celestee with my Atom HE. I wasn’t fussed on the stock cable (not the SQ so much but it was a bit stiff and I didn’t like the feel of it) so I got a Moon Audio Silver Dragon XLR cable (proved to be a bit expensive hear in the UK when customs duties were added!). I’m really happy with both headphones but especially the Clear Mg’s (with or without cable upgrade)…