I added a really good quality JBL sound bar to our Lexi for the same reason, the loud ac. To be totally honest, it really wasen't that much of an improvement. The ac still overwhelmed it, and I removed it. Still heard more of the ac then the sound bar unless I cranked it way up, and then it was uncomfortable and very noisey, the sound bar compeating with the ac. A better option might be a theater type system, but I didn't want to go to that expense.
Instead, bought two wireless headsets and with a splitter ran them from the rear outputs on the tv. Both work perfectly and we can both adjust the sound level to our own comfort level.
Just an option you might want to consider.