You might want to play with cartridge loading...
Is your cartridge a VxMR or VMR? - the VxMR has a depressed high end (Shure sold this as the "audiophile" sound profile) - where the VMR is neutral.
Either one of them will achieve the right "designed" sound if they are loaded right ... so checking the capacitance is critical....
However....
The observation has been made that the popularity of many MC cartridges is due to their artificially enhanced detail and soundstaging...
(
http://www.regonaudio.com/Stanton881AudioTechnicaATML70.html)
They are popular with audiophiles rather than recording engineers....
So just a couple of thoughts:
1) The thing that MC's do to provide that effect is they have a gently rising top end, starting at around 10k, and rising to around +7db at 20k (some rise more - very few less) - this effect can also be duplicated with very light use of a treble knob or equaliser.
2) Soundstaging is a product of separation (in conjunction with phase...) - the Stanton/Pickering family are the champions of separation.... the good ones are out of production, but patience can pay off... the Stanton 881/Pickering XSV family are excellent...
The Audio Technica VM design is also somewhat different in approach to the Shure family - an AT150MLx (current prod) or a vintage AT155LC / AT20ss / ATML180 etc might be of interest.
(I like the Shures, I use a V15VMR, they are tonally very very good, but the above named cartridges and their peers are just as good albeit different - and that difference might be what you are looking for)
3) Something completely different - take a look at the Dynavector Karat series of cartridges.... due to their very very short cantilever (around 2mm) and the use of a solid ruby cantilever, they have an immediacy and dynamics that are quite unparalleled... detail, dynamics, these are its strengths..... separation is its weakness. What this one does well it does at worlds best levels.... (would require an MC phono stage or step up)
4) The Dynavector cartridge are mostly high compliance and may do well on the black widow... their high output model 20X2H might be worth a try. (it is a much more "normal" design than the Karat)
Finally the vintage Marantz receivers have a great rep as headphone amps... I would not necessarily be looking there!
Headphones like all speakers are one of the most coloured / distorting parts of the system - right alongside the cartridge... the mechanical transducer parts of the system are the ones that introduce the biggest compromises - each designer has his/her own compromises... so they all differ... If you are 100% happy with the speaker end, and the way it responds to other sources (FM, CD...) then the cartridge should be your main area of focus - and of course the way the cartridge interacts with the arm...
HTH
bye for now
David