Update:
I'm now past the recommended 48 hour break-in period, so I thought it was time to post an update.
Configuration:
-No extra resistors added in parallel, so the cart (AT33EV) should be see a theoretical reflected load of 183 ohms. The default setting for AT33EV with the Devialet Expert is 200 ohms, so I'm going to consider this 9% variance to be "close enough" to make valid comparisons given all the other variables and vagaries of vinyl playback.
-The SUT is set for 1:16 / 24 dB gain. The cartridge outputs 0.3mV
-Following
@SIY 's calculation of 4.3mV stepped up output, I set the Devialet MM input for 4.7mV, which gives a 10% margin of error to help prevent clipping / overload
Observations vs going direct into the Devialet Expert MC stage:
Things I'm Sure Are Different:
-The noise floor / hiss has dramatically dropped. I didn't bother measuring it because it's obvious to the naked ear. At -20 dB I can't hear any hiss unless I stick the tweeters in my ear, and even then it's faint. At 0 dB I can hear hiss if I kneel in front of the speakers, angle my ear towards them from 12" or so away. In my listening seat 15' away I can't hear anything.
Things That Might Be Different (but I'll have to do some vinyl rips to know my memory isn't fooling me):
-Dynamics might be a little better. This doesn't seem crack smokingly insane if the output voltage is dramatically higher....but it might be nonsensical from a physics POV.
-Bass seems different. This seems right on the edge of psychoacoutically fooling myself (I'll have to rip to know for sure), but it seems slightly less taut, slightly more lush.
-LP surface noise seems less. How could this be? Would active gain amplify LP surface noise in a way that a SUT does not? That makes little sense to me. Is it a "loss of detail / resolution"? If so, I don't notice it on music. This could just be either my imagination or a coincidence that I've recently played a lot of virgin vinyl.
-It maybe...maybe...(I hesitate to even write this because it sounds ludicrous)...sounds slightly more like tape with a little less of the mechanical resonances that come with LP. But I'm not sure how this could possibly be true unless somehow the different electrical loading / circuit is changing the energy path in the system? But that sounds infinitesimally small, even if hypothetically possible, so I'm probably just imagining it.
If I get some time, I might make some rips if I can find a good place to post files.