What commerical audio system tweaks provide sound quality improvement??

A visit to the ENT (Ear doctor) and Audiologist (hearing tester). 

If you are using a computer to a DAC for digital, try a USB Disruptor and the accompanying USB cable, only around $170 for both. Sounds better than my $500 USB cable. Lower noise floor and can listen to for much longer periods without fatigue. Also sounds better than the Uptone Regen and much much better than an AQ Jitterbug. 

Ok, so let me ask the obvious stupid question. I know that resistance in electricity is big. The less resistance the better more usable current. I have 14g ordinary radio shack speaker wire run to all my klipsch surrounds and rear surrounds and my mirage os3 fs towers and mirage os center. Would I REALLY notice a difference upgrading those cables? 14g shouldn't have too much resistance coming from an Emotiva xpa3 and xpa5 right? But i do have custom badass interconnects 

Well badass for me. They're a 12g belden wire with silver connectors 

I have tried numerous tweaks in the many, many years that I have been into this hobby (obsession?).  Some have, IMHO, had little effect on sonics (like a green felt pen to coat the rim of CDs) while other have led to much more benefit.  My most recent tweaks were replacing stock fuses in my system with Synergistic Research Black fuses.  Amazing and unanticipated improvement in soundstage and detail.  Tube rolling can also be an effective tweak.  Also, consider replacing cables (interconnect, speaker, and power).  I have also fooled around with footers (not a fetish) but have heard only minimal improvements in sonics.  Try to audition tweaks before committing to purchasing.  Enjoy!