I don't care because I always turn it off. And I don't mean just porn games, but all games in general. Developers always put the music volume at 100% which with 38W output power of the subwoofer (trust me, that's a lot more powerful than you think, especially with ALSA and proper equalizer settings) feels like someone's ringing a giant church bell next to my ears. So the first chance I get I turn all music off. Then, if I decide I'm interested in the music, I either unpack the game and extract the music manually (if it's a renpy game or any other kind of open source game), or if it's a closed source game, I usually search in YouTube. That's how (by a YouTube search) I discovered I liked some of the music of "Saints Row The Third" with "Killbane and the Syndicate" being my favorite track.
Most of the times it doesn't really matter and I play with really low volume. But there are some games with great music that adds to the atmosphere of the scene like BaDIK. It has both great music and also the placement is really good.
Games that do have music which is fitting and not too loud really add to my experience whilst playing. For example, some moments in Eternum with Luna felt so much more emotional due to the music
Music is nice if it fits. If not I just tend to mute it anyway.
Oh and I don't care how good music is, you should definitely not make game R16 and cut lewd content in order to keep music...
It needs to fit the scene and feel. I hate music that does not change or random sound for no reason. I usually mute a game with music of it's own since it clashes too much. I listen to a mellow ambient relaxation track I downloaded years ago.
Mute everything for me always, I prefer that to listening to music that doesn't go with the situation or listening to the same music over and over again during the whole game.