Sorry this is late, I am trying to catch up reading nervosa posts. Don't worry I won't reply to every one of them...
I did a lot of research on grounding recently to make an aerial antenna safe from lightning. I am not an electrician nor an expert, so your information may eclipse mine by a long shot...
As I understand, Bryan is right about code "discrepancies". If you have a 2nd ground rod it must be bonded back to the original main panel ground rod. If an electrician installed the 2nd rod, he should have done it to get his permit signed off. If lightning strikes it will hit only one ground system first, and whichever gets hit first you will have many kV potential across the resistance between the two panels and their separate grounds causing hundreds of amps to flow, frying everything in the path and melting wire insulation in the walls! The biggest thing I learned about grounding was to bond all ground rods together with copper that can handle 10,000A for a few milliseconds. NEC requires this. If your house burned down from a strike and fire inspector saw that 2nd rod with no bond, you would be kinda sad about what the insurance company would say.

If you sell the house without disclosing non code wiring and it burns down you still pay! I am trying not to sound too serious, but maybe I am not succeeding!
Less important but also codeworthy, if your high end AC power cords go into the wall before connecting to the subpanel, they have to be approved for inwall use, like romex is. Maybe if it is run inside grounded metal conduit inside the walls you would be OK. I dunno. This is more to insure the insulation can adequately protect the conductors from shorting if wet or nail or overcurrent gets in there. Maybe years after you move away and new owner turns your audio room into a spa with a heated jaccuzzi. haha
If you find that binding grounds together add noise/hum, you could have a loop. Often it is not the power that is looped, but the signal wires. Jensen and others make 1:1 signal transformers to lift ground loops. They are pretty transparent to the signal, IMO. This won't affect your improved power response, but will cure any ground loops that might popup if you add a grounding bond. I know it is not the audiophile way. The alternative is to unplug everything in a storm and never ever forget.
I have similar positive experience with separate circuit, even though I have only one main panel. A 15A switched outlet shared with a lighting circuit is next to a dedicated 20 amp circuit. Moving the amp's plug from one to the other gives a nice improvement. 20amp circuits will have heavier gage wire inwall, which I think is a lot of the reason for the improvement, 2x more copper in the conductor lowers resistance a lot.
I have always thought that running 12ga romex from breaker to component with IEC connector on the end would be interesting to hear compared to outlet and plug. I still don't understand why the last few feet of wire in a different flavor trumps 50 feet of romex in same circuit, but I accept on faith until I learn. I think plug and outlet and wire ga. are more important to lowering resistance than the already low resistance of any decent wire.
Sorry for the wet towel about the grounding, Doug. Maybe check it out just to be safe! I have some links for parts to bond it yourself if you need it.
Rich