Dear Gxleetw: +++++ " suggestions on MM to MC upgrade " +++++
Certainly you have several roads to achieve a real upgrade for what today is the quality performance on your analog rig, not only with a cartridge change but even with a different tonearm or better phono stage.
But if you choose to go for a cartridge you can improve what you have staying with the MM/MI alternative with cartridges like:
Ortofon M20FL Super, Nagaoka MP-50, Ortofon M20E Super, Garrot P-77i, Grace F-9E etc, etc.
These unexpensive cartridges IMHO even or beats any of those MC cartridges ( btw, I agree with all those post here and I'm not trying to degrade those opinions. ) but the Concerto that I never had the opportunity to hear it.
IMHO if you want to go on the MC road and want to even or beat any of the cartrridges I name here you need to go higher on the LOMC alternative: ZYX Universe, Dynavector XV-1s, Ortofon A-90, etc, etc but these excellent LOMC cartridges needs to be mated to an excellent phono stage too.
Maybe if you tell in specific what are looking for to improve or what are your targets on quality performance be more easy to help you.
because you say: ++++++ " sounds wonderful - may be a bit on the rich side, but it sounds great to me " +++++, so you are really satisfied, many us maybe can't say: " my system sounds wonderful "!!!!!!!
Regards and enjoy the music,
Raul.