I would also like to add that more overt appreciation of Asterion's smell would also be hot. I didn't think to mention it since there's been a lot of the MC smelling Asterion (and noticing other's smells) already in the text but seeing more of it in an open and intimate way would also be hot.
It seems your musical muse has inspired a musical R&D idea for a possible NSFW: a recording studio! Not only could guest and staff use it to share the miracle of sound with the world, but it would also provide an opportunity for the MC to listen to Asterion's music in Asterion's native tongue (presumably, the hotel's translations would not apply to words being recorded and digital recordings. Also, assuming that when people sing live, the hotel translates the lyrics). This could also the be first time Asterion listening to himself in this way and his thoughts on it.
I picture the MC wanting to record some of Asterion's playing so he can have them to play while they're both working. While listening to the playback, they end up having some passionate fun in the studio while a recording of Asterion playing and singing a romantic song is playing.