Just a suggestion - I've found huge benefits by just using a drone. I don't make a big deal out of it for a while. When doing your F around the room, put on a drone of an in-tune F (doesn't have to be Harmony Director, even your McAdams can do that). During chorales I often drone the tonic note. It's amazing how much the kids just naturally fix issues when they have that reference point.
And you're not wrong about the sound quality. Seriously, for that cost, you would think they could use better sounding patches.