So this may not be for everyone. Instead of bass traps and the like, I decided to reinforce the walls of my audio room and the rest of the house by removing the cheap masonite siding and replacing it with stucco.
Ok, that was not actually the impetus for doing stucco, and I didn't expect any audio improvements, just the asthetics, but what a difference! Everything is tighter, more focused, and significantly less reverb with the clap test. Much less noise infiltration and exfiltration. (which makes the neighbors happy)
Several people have commented on it without me saying a thing.
No moral here, just something that happend, and loving the results. :D