it’s excellent, very probably the more realistic of all the SVT sims I own (hardware or software). to me it sounds and behaves more like a SVT-CL (the one with one channel and the black faceplate) , whereas the sims are often based on the SVT-VR (two channels and silver face plate - the original SVT). it’s agressive, punchy, has lots of gain, and behaves very close to an actual amp.
I think you listened to this cover, recorded with the SVT sim on the X3.
The X3 is really an impressive tool, it’s by far one of my favorite PODs. and it’s not the one we find the most easily, possibly because it was very expensive at the time. I see this preamp like some kind of hidden gem in the Line 6 range.