A Low Output Moving Coil cartridge (by virtue of it’s smaller/lighter parts) can improve LP sound, not the SUT. A SUT is not even supposed to reveal it’s existence. They are PASSIVE, no power involved.
Regarding Imaging, my MC cartridges’ channel separation and channel balance are wider/tighter than my MM cartridges, revealing measurable advantages of the differing technology.
Then there is their sound, that you may or may not prefer, i.e. is improved always better? Better for all or some of your content?
A SUT should simply serve the needs of the cartridge: step up it’s refined but weak signal to MM Phono Input Stage signal strength, (where RIAA Equalization and Further Signal Boost needs to occur) and deal properly with the impedance of the cartridge’s coil’s impedance.
rule of thumb: SUT impedance should result in impedance around 10x the cartridge’s coil’s impedance
i.e. my cartridge’s 10 ohm impedance should go into a SUT load of around 100 ohms. Load, (not setting), the settings on SUTs can be a mystery, you must know the gain and impedance specifications. My Fidelity Research FRT-4 SUT setting 10 results in a load of 110 ohms. You might think it means use 10 for a coil of 10, get 110. Well, what about it’s input marked 30, which results in a load of 141; or it’s 100 ohm input which results in a load of 423 ohms? I have yet to find the logic, anybody?
MM Phono Stages have minimum and maximum specs (sensitivity and range of signal strength it can handle without overload). It is nice if you can end up with a volume that is close to the volume of other inputs, some inputs are adjustable for that reason.
Phono Stages RIAA sound different, some have built in SUT’s, MC IN, in addition to their MM RIAA, some have independent adjustability of signal strength and impedances.
I always advise: anything phono, get return option.