Phono preamp or SUT for low output moving coil

You could get BOTH Hagerman’s Piccolo ZERO (transimpedance) and Piccolo MC (voltage drive) head-amps brand new for just over $500 and be covered for virtually any cartridge’s needs in the future (and already mentioned, "transimpedance" is not a good match for every cart, like Benz Ruby / LPS, VdH Colibri, or that Denon). Pick your favorite MM stage to pair them with, especially tubes.

Synergistic parings are hard to nail down for any given cartridge & system (ad the MC stage is where it matters most!), but these units generally sound very good and are much more flexible than the typical SUT. I’ve gotten particularly amazing sonic results from the little ZERO paired with Koetsu Blue Lace Diamond and Ortofon SPU Classic GE Mk II. The lower the output, the more efficient the ZERO is at amplification, as long as its coil impedance is going down proportionally (like with the SPU). The voltage-mode Piccolo is just a good basic head-amp - I find Hagerman's offerings here typically a bit warmer and more musical than you'd find in e.g. Herron or Audio Research, but with the caveat being a bit higher noise floor than average.  

At their prices, just add them to your toolkit lol. It’s also a good baseline to determine whether a fancy expensive SUT has good synergy to your cart or not.

In practice it is impossible to achieve, but the practical outcome is, IMHO, the same, the lower the internal impedance of the cartridge, the greater the transfer of current to the phono stage. And that is because the internal impedance of a cartridge will likely be well above the input impedance of a transimpedance phono stage.

Agree. Jim Hagerman has posted that his Piccolo Zero’s input measures 0.02 Ohms at 1kHz, noting this value is frequency dependent. Even if its input rises a bit from that within the audible band, it should still be negligible compared to the very lowest commercially available MC coils at 1 ohm. The amount of current flow should be inversely proportional to the sum of these ohm figures (coils and input), so "Close enough to zero" is what matters for these stages. If a "transimpedance" stage had an input of (say) 2 - 4 ohm, that would be a problem.

Though I haven’t attempted to measure / quantify, the 2 ohm, 0.2mV SPU Classic GM E gets a bit more net gain from the Zero versus a 5 ohm, 0.3mV Koetsu Blue Lace (and that always felt like a "strong" 0.3mV). Both pair very nicely; the Zero amplifies these cartridges very "efficiently" and subjectively sounds GREAT with them. The SPU pairing in particular is quite special. I’ve been running both of these at 1 step down from the Zero’s max gain setting (4 total levels).

Meanwhile, a 0.38mV Colibri pairing was just not good; its coil impedance is necessarily high due to its less efficient monopole design, and though the Zero can be adjusted to give enough gain / volume (at its highest setting), the subjective result was not as good compared to SUT or JFET MC stage.

Agree 100% with everything @herman said!

The Rogue Ares phono stage also allows loading a SUT at 100K or 1 MEG ohms (in addition to the usual 47K option), and has done so since its introduction ~ 2010. It's certainly a rare feature that I wish was far more common! Yes, it allows a cartridge like Benz Ruby / LPS to play happily on a SUT.

For the most part, even phono stages that brag massive loading flexibility lock down to 47K once you flip to MM mode, much to my chagrin.