Need help with phono stage and cartridge upgrade.

you have a good system.  resolving and extended top to bottom.

suggest you do both... get a good used lehmann black cube se for 400-500 and a benz glider medium for 700 (one of these benz's is on a-gon now)... 

will be a major step up in detail and refinement in sound from your current nag and mani

I listen to mostly contemporary jazz and also some folk, like James Taylor and Joni Mitchell and occasionally some fusion. My system is a mix of vintage and new equipment. My Amps are B&K 200 mono blocks with a Aric audio tube rectified preamp. The speakers are aerial acoustic model sixes. I have two Rel T/7i subs and a JVC QLY 3F Turn table and a Schiit Mani phono stage.

you need to tell us more about your system your musical tastes and what about the sound of your system you are trying to improve

then we can actually be helpful

buy used here imo