I don't think you would hear the difference in S/N ratio, as the LP itself will be noisier than any phone preamp. But you MIGHT hear a difference in RIAA response. Being able to hear a difference means that the more accurate one -the Duo- will sound different to you from the Solo. If all production versions of the Duo are actually as accurate in their RIAA curves as the one that was tested, then the Duo would be MORE ACCURATE but that doesn't mean prefer it more in an blind A/B test. You might LIKE the slight FR change that the Solo makes. The Duo is BETTER in the sense that it more closely follows the RIAA playback equalization, but it's possible that the sound of the solo might be something you like a little more. There's no way to tell except to listen yourself, unfortunately.
But if you have some reason to prefer higher accuracy- for example if you are auditioning pressings from a vinyl production line - then you might prefer the Duo purely for engineering reasons. Or, if you are like me, you'll want to own the more accurate unit because to you knowing that it is more accurate makes it more enjoyable to own. Even when I am not listening to my Topping DAC I am happy to think about how transparent / accurate it is. Ownership of gear isn't ONLY about the sound- although there is a belief that the most accurate. transparent devices will yield sound that is as close as possible to the sound that the artist intended. Some part of ownership is knowing about the gear and appreciating the technical performance that you know it is capable of.
For example, I love the fact that my $200 Topping DAC outperforms many $4,000 DACs. Yes, I like to listen to music, but I also like to own objects about which there is a story which pleases me.