Looking for help with a Benz SL low output cartridge

I also have a KC Vibe.   I recently got a Dynavector MC and it sounded pretty good with the Vibe set to 60 dB but it wasn't quite enough gain

I bought Ned Clayton's Cinemag 1254 SUT and it's great.  I set the Vibe to 47k and 40 dB and set the switches to 1:13 which seems to work well and plenty of gain.  

Sounds excellent,  I am not ready to upgrade my phono pre just yet.   When I do I will most likely be a Zesto 

With the SUT  the noise floor is lower and seems more dynamic.   

basic specs

Specifications

Gain settings: 40, 45, 50, 55 or 60 dB
Loading: 100, 200, 475, 1k or 47kOhms

IF the specific load options fit your MC cartridge, (coil impedance close to 10 or 20 or 47 or 100) I would expect it to be as good as a SUT/MM Input.

note: any SUT, the issue is the same, is there a setting for loading and gain that corresponds to your cartridge. My chosen SUT has PASS for MM and 4 options for LOMC, a faceplate rotary switch, however, the gain and resultant load are paired, not individually selectable

At a glance, I did see a few comments about 60 db gain not enough, thus IF your cartridge has very low output, it might not be the best choice.

note: load and gain settings are internal, this is not for me or others who play a variety of cartridges via quick change removable headshells. In that case, front face rotary controls are easiest, or a modern unit with remote control.

The Benz SL cartridges have an internal impedance of 12 ohms. It’s kind of on the line for a transimpedance phono stage. No reason not to try it, but only with a return privilege. You cannot use a transimpedance phono with a SUT, so it’s one, or the other. 

I use SUTs with all of my phono stages, but in your situation I would look at upgrading my phono stage, rather than adding a SUT. There is no right or wrong between high gain phono stage, phono stage with SUT, and high gain transimpedance phono, just personal preference. All can yield marvelous results.

Many folks use primary, or secondary, resistive loading on their SUTs to change the impedance. I prefer not to, but it can be necessary in some applications. The Ned Clayton Cinemag 1254 SUT, mentioned earlier, is very reasonably priced and has switches for four different impedances and gains, 1:10, 1:13, 1:20 and 1:40. Kind of the Swiss army knife of modern SUTs.

If you want to play with transimpedance, Hagerman makes an inexpensive transimpedance head amp that could be used in concert with a conventional phono stage like yours.

What line stage are you using and what is the gain?

Whatever you do, don’t mix a current driven phono stage with a SUT.  The two options are mutually exclusive. Also, keep in mind that the markings on a SUT like the one belonging to Elliot are an indication of what the internal resistance of your cartridge should be, in order to match the turns ratio or voltage gain afforded by that particular pair of inputs, as Elliot correctly intimated.  But it’s not absolutely necessary to match the values of the inputs with the value of the internal resistance of your cartridge.  There is some leeway, and you want to choose more for how much gain you really need than for matching the inputs on the SUT to the internal R of the cartridge.  For example, a pair of SUT inputs labeled "3 ohms" will typically afford much more gain than a pair of SUT inputs labeled "10 ohms".  To understand this, you might want to first understand the simple math.  Ideally you want the ratio between the internal resistance of the cartridge to be about 1/10 of the input impedance of the phono stage as seen through the SUT.  The SUT reduces the apparent input Z of the phono by a factor equal to its turns ratio, squared.  So for a 1:10 turns ratio, you divide the input Z of the phono (almost always 47K ohms for an MM phono stage) by 100, which gives 470 ohms. Just apply that conversion and you can see that a 3 ohm cartridge can in theory drive a 30 ohm input Z.  To end up with a 30 ohm input Z, the SUT may have a turns ratio as high as greater than 1:30, which is an amount of gain you will almost never need.  So you are not restricted to using the 3 ohm inputs if you have a 3 ohm cartridge. Etc. The vintage Japanese SUTs are often marked as is Elliot's, and I find it regrettable and confusing for new users.  Bob of Bob's Devices will set you straight.