The TT has already been upgraded:
Feet, dampening, tonearm rewire, outboard power supply. I’ve done it all.
Great! Another cartridge is always a good idea. Stanton 881s is a killer for the money, especially NOS, great for Technics tonearm (Kevin at KAB will tell you the same).
With two SUBs (if your room is not huge) you can only cause more problems with standing waves, if you want to improve the sound without changing your analog rib then think about proper room treatment.
I’m watching
this channel, there are so many information about room treatment, bass is the most serious problem in any room, if you have no room treatment you have to think about it first, because if you feel a lack of bass with one sub it can be a room. You can use
this calculator to see your room modes.