Met him once during Geometry of Now event he curated in Moscow (Feb 2017).
It was actually quite a funny story, daughter of officially the richest man in Russia, Victoria Michelson, happened to walk into Fell and Luke Fowler's installation at the Barbican Center and decided to offer him the chance to treat this disintegrated pre-Soviet water-power plant recently bought by her father for future art center purposes.
He invited a lot of his friends and favourites for sound installations, workshops, talks and live gigs, of course. You can check the line-up for names, some artists couldn't come, i guess, at least i know that he also invited the 'chre, but it was against their schedule (no tour at the time). He even brought some of his favourite printed texts for library section (just a large table with A4 prints of research articles and occasional books on philosophy and shit). Mat Steele was there, too, i forgot his exact role, but he was the main technical/sound producer of sorts.
I saw Mark participating in the last talk (on curating contemporary sound art and music) and decided to greet him in person. But i didn't know what to say, so i kinda stood there trying to come up with anything and finally decided to go the idiot fanboy route by asking about his kids. I already deducted that Rian Treanor was his son (i was the one who shared the evidence with WATMM and started the rumour, if you recall), so i asked for his superfluous confirmation (he just gave a nod) and then asked about his daughter, whose track he played in the Headphone Highlights podcast, she also narrated his Composing with process series on radio web MACBA.
So yeah, i'm there asking him about the track, he was ready to go into it but i already heard the story in the podcast, on to the next question with a slight interruption - what's Connie up to? And he goes on with his usual calmly drawn out talk and i'm not hearing half of it (she's twenty and?) so i interrupt him again by asking if she's making electronic music and he says no. Then some girl comes by to greet him and after a pause i awkwardly jump to the Mat Steele question (he already said about his participation in the public talk) and yeah, ok, thanks, bye go to the exit.