I’m not sure what any of you think you gain by having an extra meter and panel.
The panels aren’t magical noise filters nor do they somehow improve the power delivery.
About the best you can do is run a sub panel from your main panel to your stereo room for the thick wiring, but that still leaves you vulnerable to noise and hash at the main or from the power line. The power line itself is not beauty of a noise-free source either.
I have a power regulator at my stereo, which switches every 5 V difference, keeping my VAC at my stereo between 116 and 122 VAC all the damn time. Even with everything off it is switching to keep the voltage right. Would this be better running a thick wire all the way to outside? Only a little, in as much as the voltage drop caused by the stereo load would be minimized but there’s a lot of voltage variation at the transformer, and no amount of palladium plated, platinum core wire the size of my thigh is going to fix that.