I was conferring with my newest colleague, and explaining to him the hack job I had to do to make music on hold work. Apparently, his google-fu is better than mine, as he found this gem:

https://supportforums.cisco.com/discussion/11890741/unicast-ucm-music-hold-fails-through-cube-asr

Turns out, they did put in a “revert to old behavior” option. It’s called “Duplex Streaming Enabled”.

Needless to say, that works much better than what I was doing.