Cost Effective System Improvement?


My hobby is to get the best possible sound IMO at the lowest possible cost. My system:

Tekton Electron Speakers - Upgraded
Doge 10 Tube Amplifier (generally 30WPC in Class A) with Psvane KT88-TII, GE 5751 3 mica black plate preamp tubes, and NOS Mullard CV4024 phase inverters.
Denafrips Pontus DAC
Canare 4S11 Speaker Cables

I listen only to TIDAL Premium through Bluesound Node 2i using the BluOS on an android tablet. I often listen to vocals and use the following as test tracks:

Vaya Con dios “Don’t Cry for Louie”
Dave’s True Story “Chasin’ The White Line Down”
Dead Can Dance “The Wind That Shakes the Barley”
Harry Nilsson “Without You”
Glen Campbell “By The Time I get To Phoenix”

I would like recommendations on what I might do for a cost effective improvement. I would consider spending $2-4K for different speakers or amplifier. The speakers and/or amplifier would have to weigh less than 80lbs. My back is 75 years old.

I appreciate your recommendations.
chinook9
You listen to “only” tidal. I would start with your wi-fi connection. First thing I would do is run cat-7 hard wire and drop the wireless. Then look at Small Green Computer company and their products to bring in fiber to the signal path. When I did these upgrades for Quobuz it was night and day improvement. This will also leave you money for room treatments.
Sometimes, not always, speaker cables can make a huge difference.  I have been on both sides of this and can say from first-hand experience, Belden/Canare work absolutely fine and sometimes they can suck depending on your amp/speaker interface. I would not overlook trying out a good pair of cables.  If you're back is bad, I suggest Audience AU24s, which are excellent and easy to work with.  Hopefully your runs are not too long because it can get pricey. Audience cables are often available on the used market at reasonable prices.  I would say any generation of the AU24s are very good. 
One simple upgrade, to my ears at least, would be ditching Tidal for Qobuz.