You give extreme cases, yes put a preamp on a sub-woofer is not smart, but as a designer told me years ago, You think we don't know the effects of vibrations? Of course, we design that into our product, but you do understand the tweaks are the new profit margins of stores and they are huge. I fully understand adding this or that to one system changes the sound, that is a given in a decent system, you could take 4-hard apples and put them under a preamp and you hear a change in the system because all your doing is making a new area of resonance/coloration that will stick out more in one area of the frequency response than without. Sony whom I worked for many years made the Esprit amps and preamp, they had parts not yet used in any American gear, plus they had magnetic feet for the gear to rest on which floated the gear. So if Pass lab makes gear with the feet they do, or Luxman or Esoteric makes custom feet for their gear well they must know what they are doing but if you want to change the sound then do your best, but it is only better for your ear and no way makes it more accurate. I love power cords because with the right one for my taste it can make more of an improvement than what a new piece of gear might. Tweaks are fun, just don't make them an end-all you can put a small statue on an amp or preamp and it will change the sound without having to spend $$$ to do so because it's an audiophile tweak, please. NASA or Medical gear has zip to do with Audio that is pure marketing, and we in marketing fully understand that. Audiophile bane, and paranoia, there is always something better, or a tweak to make it better, no you can make the system sound different but no way do any of us know if it is better than what they heard in the mastering studio. That is Audiophile's many myths. The fact is we build systems to our own tastes, and that is great and worth every penny to us, so tweak away. Fuses (many so if one is right the rest are wrong)? grounding systems, dampers, and all the rest, there is something out there for everyone that why they made them for extra a profit above the cost of gear, it is a product category into itself.