Cartridge incompatibility, Soundsmith and Luxman

When you use a SUT you should use short, low capacitance cables. Under 1m for sure, ideally 0.5m or as short as you can go. It has to be low capacitance - for example, the Audioquest LP / phono cables, and their Bridges / Falls IC cables are good, but their higher end Elements interconnects are BAD for this. Cardas interconnects typically have extremely low capacitance and are good for this.

I’ve done the 10x SUT thing for a Benz LPS with 0.34mV and 470 ohms MINIMUM recommended load (it seems like it wants a higher number), not too unlike your SS but MC based. Tried a few SUTs, 8x - 10x. It was an OK result, not stellar. I feel like this kind of cart is a tough match to a SUT (all my other carts love a SUT). With the LPS, I got a slightly better result from a Hagerman Piccolo2 which is a JFET headamp that has amazing gain & loading options and only costs $289. But the best result I’ve gotten from the LPS so far is on a Hagerman Trumpet MC, which only costs $1100 new and has an improved balanced Piccolo built in. The MM stage is tube based and (mostly) balanced circuitry. It’s not as quiet and refined as my VAC phono stage (which is SUT based), and the chassis & wall wart are clearly built to its low price point, but for that tough-match LPS it gave a better result than the ~$16K of phono stage & SUT.

The resistor mod to you Luxman sounds like it might be a great idea though.

Let me repeat the option of buying a $289 Hagerman Piccolo2 as a "stopgap" for use with the Luxman MM stage - it will properly load the SoundSmith, and it will allow OP to discern if he likes the cartridge enough (I mean REALLY likes it) to keep pursuing its options. It can be sold to recoup funds at the end of experiment. Or it might sound good enough to keep in place for a while.

I used one on my Benz LPS and it handily beat SUTs which couldn’t optimally load that cartridge into my VAC Renaissance SE phono stage. No, on even ground its circuitry isn't gonna match the refinement of OP's Luxman or my VAC, but it will beat the crap out of any loading mismatch!

Mine arrived in a week from Hawaii. Like British Mullard tubes, it might not be what you settle on, but it’s a handy addition to your audiophile toolkit.

Most low/medium output cartridges with a typical 0.4mv - 0.6mV output and ~ 5 - 10 ohms coils should work well with that Luxman MC phono. The carts like the SS Zephyr and (I'm guessing) Benz LPS / Ruby / SLR are the outliers that have any trouble. There are a number of MC phono stages that only offer a 100 ohm load, since it's a very typical value in this range. 

@lewm is right, he never advocated a SUT here. I don't think anyone was suggesting that, except OP. I touched on cable requirements for a SUT, but to be clear I definitely wouldn't try to throw a SUT on this thing (the JFET headamp is another deal entirely).