relating to this quote:
"Otherwise, do what actual music and sound professionals and amp designers do…ignore the nonsense of silly and fraudulently marketed psuedo tweaks."
I would like to say that amp designers have a completely different set of requirements to work against. They are working against limitations on cost and manufacturing processes. They need to weigh the availability of individual components when the equipment is actually manufactured or assembled. The idea that a Hi-Fi Tuning fuse can actually improve the sound is valid, but when it comes time to have these amps/equipment built on time and on demand so that they can ship to their distributors/retailers, the available of individual components becomes critical. What happens when a set of fuses are not available for weeks? A company like Bryston/Classe is not going to be able to wait to ship 20-50 units. Also, cost of every single component adds up and the company's goal is always to use the cheapest components that allow them to meet a certain threshold (difference between a $4 Littlefuse and a $60 Hi-Fi Tuning becomes significant).
However, we also have companies like Audio Note or Audio Research who do focus on actual individual components (even down to what kind of carbon resistors are used or the type of solder). However, their manufacturing output is a lot less and item cost is a lot higher.
Music and sound professionals have an entirely different set of responsibilities and don’t have time to be critical about every single piece of equipment. I’m sure recording studios have something like 2-5 million dollars of equipment (tons of devices - racks and racks of equipment) and need all their time to focus on recording/mixing/effects/etc. They need equipment that is good enough to meet the bottom line, but they are not going to spend another 1-2 million and hours of time when "off the shelf" equipment is going to be decent enough to produce their product. In their industry, time is money. Unless your Cookie Morenco, who has tremendous focus on how individual components and wiring affect the sound. However, that is a very small niche market.