Responses from squared80

Looking for a true upgrade in sound quality
No mention of acoustic treatments, speaker placement, or straight up better speakers?  
Is the idea of audiophile listening a dying concept as boomers die off?
People get turned off by the snake oil. I'm glad some of that is going away thanks to science and more accessible A/B testing.  
Need recommendations on 15ft speaker cables
Just get any 12AWG cable, or even 14 or 16 for that length. You will NOT hear any difference between any OF Copper wire. Heck, you could use a coat hanger. So don't waste your money unless you're wanting something that 'looks nice', because perfor... 
Requesting opinions about 4 specific amplifiers
@soix someone's triggered. And in denial.  
Audioquest or Nordost for speaker cable
It doesn't matter. You won't hear any difference whatsoever.   
Requesting opinions about 4 specific amplifiers
@soix doesn't know the difference between objective measurements and subjective opinions. Sit down, son. You're embarrassing yourself.  
Requesting opinions about 4 specific amplifiers
Why not just get a Buckeye Purifi. Objectivity better than any you've listed.  
A stupid question(s) about power cords
You'll be fine with either. And, newsflash, you will NOT hear a difference besides one caused by confirmation bias.  
Power cords: does length matter?
Nope. Next question.  
Surge protector
If you don't have a whole house surge protector like the Seimens FS140, you're doing it wrong. Nothing else will do much, but SurgeX is probably the best outlet style protector.   
Full loom of the same cable brand vs mixing and matching.
The only thing that matters is it's copper and the proper gauge for the run length. That's it. You could use coat hangers.  
my own experience with Tekton Design
The OP must be Eric's burner account, trying to repair his reputation. FAIL. Tekton is dead to me.  
Surge protector
Surge protectors are a waste of money. Invest in a whole house surge protector like the Seimens FS140 and be done with it.   
New expensive power cord for amp and no change in sound?
Enjoy your snake oil. Anyone who says high priced power cords or speaker wire changes the sound is lying, ignorant,or a victim of confirmation bias.  
Wire break-in safe without speakers?
You'll be glad to know that cable break-in is a total myth. Carry on!