Can I use a step up transformer?

Investing in SUTs depends on how good is your phono chain and of course the system at all.
Using high efficieny speakers is an add on in my opinion as well as a good reproduction of high but also low frequencies.
Let me state in a somehow provoking way: it makes no sense using SUTs which allow you to harmonise the sound but also push it in the more stable and deep sound producing way when you have a mediocre table and phono stage. 
The good news is: today not so many real audio afficionados stick to a mediocre phono line and system. Good systems deserve using SUTs! The more excellent MCs you are using the more you understand the importance of SUTs. 
I like my MMs too. I am sure I will never convince someone of SUTs who is running MMs most of his listening life.
There might be some exceptions 🤗

One advantage of using an SUT (which I've never seen mentioned) is the ability to now alter the loading just as one can do with a MM cartridge.
Because the SUT plugs into the MM input of the phonostage, I can dial in a Resistance anywhere from 10K Ohms to 60K Ohms and the cartridge responds in the same way that a MM does.
Now I don't understand the science behind this and hope that others here can explain what is actually happening......but it works a treat on taming an aggressively bright LOMC and conversely, one which may sound slightly recessed or shy?

Dear @halcro : Please read very carefully here:

https://forum.audiogon.com/discussions/can-i-use-a-step-up-transformer/post?postid=1342503#1342503

because those changes in quality performance level comes from the very complex interaction that produce impedance/inductance internally in the phono stage that can’t handle with aplomb it, not comes from the cartridge that is non-sensitive to those load impedance changes. Problem is in the phono stage that comes with some kind of " faults " by design.
Obviously that in an active high gain PS this kind of design is not for use with external SUTs so it’s not a design faulty, the designer made it to use it in the active high gain and not the other way around . The designer in your unit never imagine that some one will use the MM stage along a SUT, so there is a " problem " in that MM stage. 

The designer of your unit knows very well what I'm explained in this thread and that's why he left in the active MC high gain stage  a fixed 220 ohms impedance that you can't change it because is not need it to do it.

Please read it.

Regards and enjoy the music,
R.

If phonostage gain not enough, investing to higher output cartridge is wiser than to SUT. That's where math easily replaces all the science behind.