Well, it’s not a pre amp it’s an integrated. Which SN, by comment consent the SN2 and SN3 are more musical performers than the SN1. In any event you’ll find any of the SNs more powerful and capable performers than the 5si.
I have not used a 5italic but did have a SN 2 at one time and do believe it will drive your Monitor Audio SE20 Studio 25th Anniversary without any issues. You can see if a dealer will let you have a home demo or arrange to bring you speakers into the dealer.