And the biggest influence on sound quality is...

The last thing I changed.  (if I got it right)

Seriously, though, I'd have to say speakers.  Every time I change speakers the system gets VERY noticeably different.  I've made small, to the extent I can, modifications in the room and there is impact.  But admittedly I'm limited.  Bride has nixed taking out the wall and the stairs on the other side of it.  Also, won't let me blow out the bedroom upstairs so we can have a higher ceiling in the listening area.  MAN!

Amps have peeled back layers, brought more speed and clarity and with them nuance.  So have wires/cables.  The Holo DAC was both subtle and powerful.  The Townsend speaker bases were the biggest surprise.  They very noticeably impacted the treble, ion a good way!  Still don't understand that.  Are speakers the most important thing?  I don't know.  But I'll say, in most normal situations, the speakers have the biggest impact.

These kinds of questions are like asking what it the most important part of a bridge.

None of the gear changes have had that much impact on sound quality.

Seriously?  What gear changes have you experimented with so far?  I have heard profound changes with different pieces of gear.  

Besides quality of the recording , I feel the quality ofthe front end is a bit more important then the Loudspeakers , for once the audio signal is converted good or bad it cannot be improved downstream, you only get one chance to define its sound character. I have been experimenting with some pretty good dacs.

that have. Changed the norm in what to expect and  just under $9 k retail ,that can 

stay with dacs that are 50% more expensive ,hint from Europe.

I see the point and can't disagree.  Once a system has good, revealing speakers, the impact of changing the front end can really change the listeners experience.  And I forgot about the recording.  Even on a mid-fi system, a poor recording or poor engineering of a recording can annihilate the music.  And the better the audio equipment, the worse that thing will sound for sure.  I guess if someone has a lousy recording of music they really like they could scout around for an old Radio Shack stereo.