It usually starts with amplifiers, then speakers, then source equipment... and then they start rearranging furniture, tearing out drywall and putting absorbers everywhere, and then it starts all over again in a cycle.
I find it best to stick with a nice comfy pair of headphones and keep expectations low for everything else. If you're only managing the volume of air between your ear drums and the headphone cups-- that can be done to an obsessive level for vastly less cost (and without divorce) than if we're talking about a whole living room.
I knew customers who built the foundation of their homes around speaker placement, having separate foundations for their towers so that fewer resonant effects from the house would impact the speakers. Haha. Madness is right!
And that $500,000 number is easy when you’re dealing with those circles for sure.