1st: I completely agree, simply change the stylus on your MP-150 Body to the 500.
https://forum.audiogon.com/discussions/who-is-using-nagaoka-phono-cartridges?highlight=nagaoka
Are you able to align/calibrate your cartridge? Near KAB? I'm walking distance from KAB in the Sleepy Hollow/Netherwood Heights historic district, Plainfield, NJ
excerpt
"knotscott
I picked up a Nagaoka MP-150 last spring, and added the JN-P (MP500) nude line contact stylus on boron cantilever to it, and think it’s spectacular. Incredibly musical with beautifully refined detail, amazing midrange clarity and separation. It sounds like I have wanted all my other carts to sound since getting into this in the early 80s. All in for ~ $570...not cheap, but not outrageous for the sound I’m getting"
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next, maximize imaging by improving initial sound wave distribution/reception. create a virtual system on this site, post some photos, so the ideas of across the width or down the length and your equipment/furniture/you didn't mention video? are easier to understand, suggestions will be easier to make and understand
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future changes
speakers, I would forget all/any subtle modifications for now,
re- arrange things so you can have larger speakers, 3 way placed/aimed best toed-in/tilted back to minimize floor/ceiling/side walls reflections (slanted face design/mid height on slanted stand/ or taller floor standing flat face slanted back to aim tweeters at seated ear level)
my assumption/guess: a small 5.1 home theater/music combo system, AVR with FRONT pre-outs, does the Cambridge have a home theater bypass input?
room treatments, maybe, but start simply with an easily re-positioned area rug
Toe In Alternates, Stereo and Video