Okay – this isn’t something we can officially support at this time, so I understand that it’s not working as expected in OSMC.
But I don’t know why you’d make such modifications, so it is hard to advise. Given that you weren’t aware that OSMC already builds Kodi with ALSA support and supports BT -> DACs, I’d advise reverting any changes you’ve made and seeing if what you want to work works without any modifcation.
Unfortunately I don’t have any suggestion at this time. If you modify the audio stack in OSMC it’s not going to necessarily work as expected.