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.