Can't help but think that the best possible upgrade would be to lose the cabinet, replace with a HiFi rack, bit of room treatment in the corners & maybe behind the speakers, and let the speakers breathe more given the space limitations. No new cartridge, new amps etc. will come close to this upgrade IMHO!
Mana Acoustics Racks / Bright Star IsoNodes Decoupling >> Allo DigiOne Player >> Pedja Rogic's Audial Model S DAC + Pioneer PL-71 turntable / Vista Audio phono-1 mk II / Denon PCL-5 headshell / Reson Reca >> LFD DLS >> LFD PA2M (SE) >> Royd RR3s.