Iāve had both S400 and S500. They are pretty similar, but I felt that the 400 is a bit more transparent and ā3Dā sounding, if that makes sense. Maybe due to the simpler design, idk. I ended up selling the 500 and keeping the 400.
But I also think it depends on what you are using it for. I use it for slaving my old Mesa Mark amps and want as little colorization of the sound as possible. When using the slave output on the Marks it slaves the whole amp, so youāll have the graphic EQ on the amp as well.
I imagine the S500 is better for preamps since youāll have the deep switches.
That being said, they are both awesome!
I havenāt tried the VHT, but regarding Coliseum VS S400 I think they are pretty similar, even when running only one side. Each side is 200W, so itās actually a bigger power section than a Coliseum. The feel is better on the Coli though. But the punch is very similar.