The Zstage is close to transparent having very little to it and being voiced with this in mind. This leaves signature adjustments to you with the tube you choose and the cables you use, both of which having minor to significant influence on the sound depending on the choices and quality you use. If you get a good transparent switchbox, you add its sound influence and one more IC. This can be good or bad depending on how you like their influence on the sound, but could be done pretty well with good cables and a good switchbox I suspect....The tube and gain will be your biggest tools though, and yes, they can potentially bring a lot of sound adjustment potential and musicality to all your system components.

I do not have a CSP2, but there are many comments on it in these forums...if two inputs are enough (or if Steve could add more???), it may be worth looking at, weighing in the cost and sound of another IC and switchbox in comparison to the cost of the CSP2 alone.

On the other hand, the Zstage is nice and neat...little, sounds great and only one tube to maintain and roll giving very easy flexibility in sound choices....that one tube is fun and with only one you can experiment a lot relatively inexpensively.

Of course you could do this with the input tube of the CSP2 also!