And the biggest influence on sound quality is...

@troutstreamnm , I have often just threaded a couple of AN fittings together and made a  (to borrow from you) makeshift pipe with a small bowl, and nirvana always followed.

One thing that we cannot fix is the quality of a recording, and I would, perhaps, argue that a good system might make a bad recording sound worse than a system with certain limitations (e.g. a soft system top end taming a hard recording).  

Also, my ability to optimize my listening room is very limited as it is my Living Room, and has to function as such.  I think it is not too bad, it is a large room, about 20x36.  My speakers are 10 feet from the back wall, my listening couch 12 feet from the speakers. The usual living room furniture,with heavy curtains that can cover the windows.

Therefore, I'll offer up thoughts on relative importance of components in the goal of reproducing excellent recordings optimally.

The hardest things for a manufacturer to get right are probably the mechanical components: viz. the speakers and turntable/cartridge combination.

Then to my mind the DAC is critical.  If we compare digital ca. 1985 and 40 years on we are living in a different world.

Pre-amp and Power Amp obviously affect the sound, but, after a certain performance level, at a second order of sound quality differences - and often in subtle ways.

Cables do have different effects on the sound, but, after again, after a certain level of performance, the difference between well engineered cables is (to my elderly ears) very subtle. 

Without really thinking this through my own components reflect, perhaps unconsciously, my thoughts expressed above.  My pre ($3.5k LA4) and pa ($5k XA25) or my home brew 6SN7 300B balanced($5k) are dwarfed by the $55-60k on DAC and Speakers.

Replacing my pretty good Audio Physic Virgos with the outstanding Rockport Atrias was startling, then replacing the good Esoteric X-03SE with the K-01xs was another significant level of improvement.

I do admit I'm contemplating upgrading the DAC to the K-01XD.  I'm hoping I can find a dealer where I can take my existing unit and compare with the XD.

I was going to say your room.

1. Attitude. I've been moved to tears listening to music on a cheap transistor radio.

2. Speakers. Assuming you have a reasonable set up (whether inexpensive or otherwise), better speakers will make the most obvious improvements.

3. Room. I'll venture to say most people have little control here, and are unwilling to move their speakers or spend enormous sums on room corrections. For those who are willing, a good room can make a mediocre system sound good and a good system sound great.

Brain!  Can't say how many times I've just been driving down the road listening to the mediocre system in my pickup truck enjoying the heck out of music.  Ear/brain adjusts to quality. 

That's not to say audio quality isn't enjoyable.  But I would hope most folks wouldn't turn off a mediocre radio if the tunes were good!