I don't have a separate Modwright preamp, but I have a Modwright KWH 225i integrated amp (which has a tube input section) and also a Modwright PH9.0XT phono stage.
Im my system, I'd characterize the "Modwright Sound" as authoritative and muscular. The low end, particularly, is extended and extremely well-controlled.
This "authority" also helps locate instruments firmly in place within the sound stage.
Compared with my previous NAD Masters M32 integrated amp and Simaudio Moon phono stage, the Modwright pair sounds fuller and more powerful. It's not just a "tube sound," but a hard-to-describe sense of "filling the room and precisely delivering the sounds of instruments and voices."
I have no idea if the Modwright preamp would carry this effect over to your system, however.