Will Step Up Transformer Improve the Sound Quality?

I have various SUTs, special Headamps, High Gaing MC phono stages (with adjustable gain), MC phono stage with built-in SUT is the quietest of them all ... 

What is really special is Current-Injection type of MC phono which I also have (for low impedance MC).

I like simplicity, less wires, I would like to use just one box instead of two. 
But if you like different flavors you must try what you like in your system! Don’t ask others what you will like. 
If you want to try a SUT there are so many top quality SUTs from the Japanese manufacturers, inexpensive classics from the 70’s, 80’s. 
If your cart is low impedance try Current-Injection type of the MC phono stage instead of the SUTs

I have various SUTs, special Headamps, High Gaing MC phono stages (with adjustable gain), MC phono stage with built-in SUT is the quietest of them all ... 

What is really special is Current-Injection type of MC phono which I also have (for low impedance MC).

I like simplicity, less wires, I would like to use just one box instead of two. 
But if you like different flavors you must try what you like in your system! Don’t ask others what you will like. 
If you want to try a SUT there are so many top quality SUTs from the Japanese manufacturers, inexpensive classics from the 70’s, 80’s. 
If your cart is low impedance, try Current-Injection type of the MC phono stage instead of a SUTs

@chakster 

We ask for opinions of people who have experience with different options (in this case SUTs vs electronic gain) in order to gauge if there is a good reason to try them.  
That is what this forum is about ! 

Dear @pg62  : Well,  your speakers crossover at 800hz and evev that looks that those drivers/woofers are a good design you can achieve even better quality performance levels from your room/system if you lower the inherent IMD ( Intermodulation Distortion. ) on that woofer.
Tha's mean to use your subs haddled frequencies below 80hz-90hz and at the same time that the Spatial speakers runs the frequency from 80hz-90hz and up. You will note an improvement all over the system frequency range and you can do that with an external active crossover as this one:

http://old.bryston.com/products/other/10B-SUB.html

It's worth by its high rewards to do it and you have nothing to lost. It's a very good learning audio/MUSIC experience.

Here you can read about those advantages when we add to our system subs as you already own but that you are using in different way:

https://forum.audiogon.com/discussions/do-you-think-you-need-a-subwoofer/post?postid=310058#310058


R.

@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.