From my experience with their Studio line I think it's fair to characterize these cables in general as neutral and transparent, and they seem to just pass everything through a system as is. That is to say, I don't think they're a good choice if you're looking to add or subtract something to the sound of your system (i.e. tonal bloom, softer highs, etc.). From what I've read of the SEI series that would seem to be the case there too, although I've never heard them in my system.
Where I find Stereovox interconnects in particular to excel is in the area of soundstaging and three-dimensional, holographic imaging. If these characteristics are important to you then Stereovox is a must-hear. I've had other highly-touted cables in my system and none have approached what the Stereovox wires achieve in this area. It took me a little while to recognize it, and it may be very system/listener dependent as is the case with all cables, but once I heard it there was no going back.
Hope this helped and best of luck.