McIntosh MT5 tonearm swap out?

Balanced operation properly executed is bound to be marginally quieter than SE operation, all other things being equal, because of Common Mode Rejection, if for no other reason.  That difference may or may not be audible if SE operation is already very quiet.  So your single experience does not amount to a definitive judgement. For one example, did you re-wire the connection from cartridge to phono input before comparing balanced to unbalanced mode? Was the balanced mode achieved using the optional XLR inputs of your PhonoBox? I can and do live with SE phono in one system and in balanced phono in my other system. But if balanced is readily available, I would advocate for using it. Just saying. It costs practically nothing if the phono stage offers balanced operation.

FWIW, I tried balanced vs. unbalanced on a PhonoBox DS3 with an AT OC9XML and found there to be no discernible advantage to the balanced connection. It was noisier than I liked either way.  I switched to a different turntable using unbalanced and it is now quieter than either was before. So proper shielding and grounding seems to be the more important thing. If you already have that, why screw around?

Thx for your response - just thinking out loud on this one...  Do you feel that a balanced 5pin combined with the Pro-ject balanced phono Pre amp would be an improvement (from current RCA)?  I have no complaints on the current system, but always looking for that little bit extra.  Running all Mac gear, C53 pre - MC601 monoblocks & do have a Pro-ject phono box RS2 preamp as well.  

All tonearms can be wired for balanced operation if that’s your goal, including whatever comes with the MT5.