Really good home electrical wiring.

I agree with the above posts, but recommend avoiding the Wattgate outlet in favor of the Hubbell. The Wattgate is a stock (hardware store variety) outlet, made by Leviton, and plated gold to look good. The Hubbell is actually manufactured from the start to be a superior electrical product, and sounds better, in addition to being manufactured with heavier and superior quality materials.

If I read your post correctly, looks like you still intend to order the Wattgate AC outlets. Is this correct? In response to your question about THHN, I think the insulation (and tightness of same) is perhaps superior to Romex. However, THHN is generally stranded, and when used for AC power distribution, sounds inferior than solid core Romex. I do use the THHN stranded in my system, but it is exclusively for the dedicated ground from each Hubbell AC outlet, to a ground rod. In that case, the stranded offers some advantage in bleeding off microscopic RF, EMI and small current leakages. On the power side of the situation, I avoid the stranded THHN for the same reason, I prefer 120 V, 60 HZ, without encouraging these same artifacts to enter through my systems power supply. I have no comments on the isolation transformers and line balancers, as I have no experience with them. I can say that I have tried dozens of line conditioners, filters and name brand transformers, and in my system, they all degrade the sound. This could reverse if you lived in a building where multiple families share the same electrical service. In that situation, the quality loss from inserting these devices could be less damaging than the gain of removing all your neighbors noise and ground problems. By the way, the name Romex is a registered trade mark, just like Kleenex and Band Aid. This is a brand name for a particular sheathed multi conductor solid core electrical cable. My last word of advice is to use this actual brand name, or another of equal quality. The no name cheap rolls of cable at the discount supply are a poor investment when you consider the cost of labor to install and the price of your components.