Looking for help with a Benz SL low output cartridge

This is a matter of taste.  You do not NEED a transformer to enjoy your Benz SL or any other low output cartridge.  You might or you might not prefer the sound either way.  Can you describe what you are hearing?  What do you like?  Is there something about it that you are not happy about?  If you decide to try a transformer, you will also require another set of phono cables, preferably identical to your main pair.  So, this can be an expensive proposition.  Please note, I personally like SUTs, am not trying to discourage you, but being realistic, these things are an expensive accessory that is absolutely not essential to your enjoyment.   If you definitely want to pursue SUTs, a good starting place would be to take a look at Bob’s Devices.  Bob is knowledgeable, reputable, I believe offers a trial program, and his SUTs sound very good and are not over priced.  I have one that he sold me that I use and enjoy that cost approximately 1/5 as much as another very good German one.  I can’t honestly say one is better than the other.  I can't honestly say that either is better than just going directly into a good high gain phono stage either.  Different, yes, better, like I said, that is a matter if taste.  

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.