I bought a book last night from Loose ID that has a long M/M/M/F sex scene in it, from the F POV...4000-5000 words. I actually plopped it into Word and counted the name usage frequency.
The example that I gave previously (400 words, 32 times) had a frequency of 1 name for every 12.5 words and was just...awful. (And it was in a highly rated review for the book; go figure.)
This one has a frequency of about 1 out of 20 words being the name of one of the three men, which still *sounds* like a lot to me, but it really worked for me. It surprised me, considering it was close 3rd person in the
woman's head, but I think that actually may have made it easier...she (the author) could take a break for a second and just concentrate on what Lena was thinking and feeling. I think you could do the same thing in a M/M scene, though, give the reader a break from the physical action into the head of your current character's POV.
Lots of he/his/they/their and an occasional "someone"

but at no point did I have to re-reread something to figure out who was doing what. Not an epithet to be seen, almost no description of the guys by hair color/eye color/whatever. Just skillful writing.
She (the author) often seemed to anchor the "who" in one sentence, using the name, then have another sentence or two using he/his.
e.g.
Matt arched forward, sliding through the slippery mess where she and Giorgio joined. With a sound almost like a purr, he coated his shaft in her fluids. Then he pulled back, positioning himself for penetration.
There are paragraphs that are riddled with names, but even they work, partly because of the way it is a chain of events, not just "Jack did X to Fred. Fred did Y to Jack."
e.g.
Giorgio’s eyes were closed tight, and he arched his head back to rest against Kenji’s forehead. Kenji threw his arm across Giorgio and Lena, feeling around until he found some part of Matt to grab onto. When Kenji used the extra hold for leverage, Giorgio cried out and pushed harder into her dripping wet heat.
Sometimes, she sort of mixed it up (these four are witches and have a psychic connection):
The edgy, almost painful tightening around Matt’s balls served as her first hint she was falling out of her own body and into theirs. For a moment, she was Kenji -- felt him shiver, straining for control as he pressed deeper into the delicious embrace of Giorgio’s ass. Then she plummeted into Giorgio’s thoughts, felt his stomach clench up around the raging inferno inside him as he counted under his breath, trying hard not to get there ahead of the others.
Anyway, it wasn't until I'd finished the scene that I realized she'd pulled off just what we had been talking about in this thread. It was done smoothly enough that there were no distracting epithets, not too many repeating names, and no confusion.
Thought it was interesting. I guess it proves to me that it *can* be done.
Off to buy the second book in the series, to reward myself when I'm done working tonight - nice long stories, just how I like 'em.
J.
P.S. Book is
Nature's Pentacle by Eden Rivers. Don't love the title, but it had a pretty entertaining story.