But you can sell them
Preamps is something I haven't tested much, but I'm frankly happy with my 18NS.
I did hear the Soulution 720 with my 108, driving Magico Q7, and it was very good, a tad better than the 18NS actually. A little brighter overall, with more transparency. But unfortunately I only had time to play a handful of songs. I might get the chance to test the 720 again.
I wouldn't bother with this 520, and go straight for the 720, before Soulution decides to put switch mode power supplies in all their models. It's only a little cheaper than the 18NS...
alexandre