Roxul "Safe n Sound" was the original plan and I bought a pack to see how it handled. By the time I was ready to insulate the ceiling, I found some measured data that showed that R19 pink insulation performed as well or better than the Roxul insulation. In a wall with only 3.5 inches the Roxul outperforms the fiberglass, but in the ceiling where I had more space the performance difference vs cost just wasn't there.
The best thing I did within the joists was to cover four A/C vents with putty pads to seal gaps and add mass to the four vents that feed into the rooms directly above the listening room.
Those doors are one concession I made to appearance over performance. I wanted the doors to match all the other doors in the house so I built communicating doors. There are two hollow core interior doors separated by about 2.5 feet. The framing for the door at the listening room is decoupled from the framing for the door to the stairwell and I've sealed both doors with weather stripping. I think you're right that solid core doors, or at least one acoustically sealed door would be an improvement, and I might put one in if I can find a style to match.
Interestingly there's a solid exterior door in the room and when I stand on the deck at the back of the house I can easily hear what's playing downstairs - so maybe that's the next door to address.
No moving now!
QFT!
