Cartridge upgrade for $600

Which MF? How much gain in the phono stage? What input impedance values are available on the phono inputs?

Without knowing those specs any MC cartridge recommendation would be about as useful as recommending tires without knowing what car they're for or where it will be driven.

Musical Fidelity A3.2 Intergrated with phono:
Input sensitivity: 250mV (line); 2.5mV (MM phono), 350µV (MC phono). Input impedance: 220k ohms (line); 47k ohms (phono). Overload margin: 26dB (line); 24dB (phono). Channel separation: >70dB, typical.

In that price range, I would suggest you consider remaining in the MM or MI domain. Low end MC cartridges are not necessarily going to be superior to any of the better ones. You could just move up the Ortofon line or consider a Sound Smith MI cartridge that meets your price limits. There are literally dozens of good choices available to you.