Will Step Up Transformer Improve the Sound Quality?

@pg62 , REL does what most of the subwoofer manufacturers do. For reasons of cost and complexity REL designs it's subwoofer to be integrated in under the bass of the main speakers. There is no high pass filter at all on the main speakers. This is problematic for many reasons but the single most important reason that this is a bad way to go about it is that you are missing out on the tweak of a lifetime. Your speakers have coaxially mounted compression drivers which your 15" mid/bass drivers cross over to at a high 800 Hz. Low bass requires even a 15 " driver to make long excursions. This wastes power but more importantly adds very significant amounts of Doppler and IM distortion to everything else the woofer is carrying and in your case it is carrying a lot! If you get a proper two way crossover and cross to your subs somewhere around 100 Hz your system will improve so much that your wife will notice it. Seriously, women are very sensitive to distortion. 
The best analog crossover is probably the JL Audio which is pricey but here is an excellent 4th order Linkwitz Riley cross over for $190 
  https://www.parts-express.com/ART-CX310-2-Way-3-Way-Crossover-245-880?gclid=CjwKCAiAyc2BBhAaEiwA44-w...
you will also require one more set of interconnects. 
There is one even less expensive way to to it and that is to use the crossover in the RELs for the subs and get the appropriate sized capacitor and put it in series with the input of your amplifier channels. In order to do this correctly you need to know the exact input impedance of your amplifier.  The equation is Fc = 1/2piRC. Fc is cutoff frequency or 3 dB down point, R = resistance(impedance), C = capacitance in Farads.
Turning this around C = 1/ 2piRFc. Lets say we want a crossover at 100 hz and the input impedance of the amp is 20 Kohms. 
C= 1/ 2pi20,000 x 100 = 1/12,566,400 = 0.00000008 Farad or 0.08 microfarad. That would be one of these. https://www.digikey.com/en/products/detail/panasonic-electronic-components/ECW-HC3B803JA/7567997
That will cost you $3.00 for two of them. 
Putting them in the amplifier is no big deal if you know how to use a soldering iron. You identify the wire going to the positive post of the input jack. Heat it up and lightly tug on it and it should come right off. Connect one lead of the cap to that post and the wire you just took off to the other lead of the cap. Make sure nothing can short out before you close up. Done. It might take me 20 minutes to do an amp. I'd be happy to work through it with you if you want to give it a try. You can always return the amp to stock configuration. The electronic crossover would more than likely sound better because it will roll your speakers off faster 24dB/oct vs 6dB/oct for the input capacitor but I think the capacitor will make a decent improvement. When I first started with subwoofers back in 1978 we were all stuffing capacitors into our amps. The very first subwoofer crossover the Dahlquist LP 1 came with a package of 30 or so assorted capacitors that you could put either in the LP1 or in your amp, made no difference.

@rauliruegas Darn rauliruegas, you stole my thunder! Good for you and you are right on the money in every way. Now you know about the capacitor trick and i won't have anything to add:-(

I love my SUT's and have a small collection of 6, but certain cartridges pose a challenging electrical match for a SUT when your MM stage is fixed at 47K loading.

One example is the Benz Ruby / Gullwing / LPS. These have an output of only 0.34 mV to a (relatively quite high) coil impedance of 38 ohms. And your DV Karat is spec'd very close to that: 0.3mV at 32 ohms.  An ideal SUT ratio for 0.3mV is the range of 15x - 20x step-up. Let's take 20x gain - into 47K, which makes a reflected load of 118 ohms back to your cartridge. Most "rules of thumb" will say you want at least 10x load-to-coil ratio. In this case, 118 ohms / 32 ohms is only a ratio of 3.7x. You're going to be throwing away 2.0dB of cartridge signal in this scenario from Ohm's Law (and hence the noise floor creeps in that much more), and also probably introduce other sonic aberrations that the cartridge designer didn't intend. 

I've successfully used as low as 6x load-to-coil ratio, but it's still not optimal and some cartridges will object to that more than others (Koetsus seem relatively well behaved as low as 6x). Below 5x is really asking for bad sound. BTW I've also tied the Benz LPS into a SUT and it just will be nowhere near its potential at 47K loading, no matter the SUT ratio (I have several to try). 

Now if you had phono stage that could run higher than 47K load in MM mode, then you could "fix" this problem. A load of 100K with a 20x SUT reflects back 375 ohms. 375 / 32 = 11.7x. That's OK! The Rogue Ares Magnum is one example of a phono stage that allows loading well above 47K in MM mode, but unfortunately this feature isn't nearly as common as I'd like it to be. 

So in short, I'm normally one who encourages SUT experimentation (even after college), but not with certain cartridges without the right MM loading options. In your case, I'd pass on the SUT. 

op

short answer to your question is maybe, but likely not too much, your phono stage is good...

for your setup i would suggest a better dynavector cart up the line... more of everything good...

have fun -- good luck

Great feedback on the SUT and crossover.  I understand about a third of it but that is o.k.  I've got some homework to do.  Thanks all.