I've been listening to HEKv2, Utopia, Ether Flow, HE-560 & HD-6xx from my Opus#2.
I was thrilled with the P2/Utopia combination. I think the Opus#2 might be a tad brighter, maybe leading to a slightly fatiguing sound with the Utopias, but I'd really have to A/B with the P2 to come to a firmer opinion. Unfortunately, my Plenue 2 is in Korea being repaired (loose/sloppy 2.5mm jack) so I can't compare. Could also end up being 'too close to tell the difference'.
Note all this listening is done via short (4 or 5 feet) 2.5mm TRRS terminated balanced cables for use with DAPs. I've got a 4-pin XLR to female 2.5 extension which I use out of the Violectric amp.
I could compare the Opus#2/headphone combinations with the sound out of my desktop rig (Sonica DAC > v280, balanced interconnects). Any particular pairings of interest?