[basementjack]

I think you have all the bases covered.

if this is going to stay as an unfinished garage, I'd put a piece of fiberglass on the floor when you're listening, instead of the rug.

as long as your ceiling remains unfinished you won't have the usual first reflection point problem you usually would.

also since there's nothing behind the speakers, the insulation behind them might not be doing much - you might try moving those pieces to the sides - directly to the left and right of the speaker and just in front...

so long as this is an unfinished garage, there shouldn't be much need for a bass trap.
if your intention is to build a permanent wall over the exiting garage door, then it might make sense to stuff that 10 inch space with insulation.