My bet would be acoustics too.  I have a client with documented hearing loss.  He's got a beach house and a canyon house and I've installed two identical surround sound systems (one at each property).

The beach house is a dedicated media room with acoustic treatments from RPG that were engineered & installed during construction.  This house was completed first and he loves the room and thinks it sounds great.

The canyon house has the exact same speakers, amps, pre-amp & sources, but it's located in an open Great Room with plaster walls, wood flooring and lots of windows and sounds terrible.  The reverb time in this room reaches almost 3 seconds and he has a difficult time understanding dialog.

I set the expectations about how bad it would be when the house was in the design stage, but he was still surprised at how much difference the acoustics made.