It would be helpful to know components involved to make a recommendation, I understand you are going from a KT88 o 805 based amplifier. Also, what speakers are you using ad what is there rated efficiency?
As Lon stated the backlog for new Decware product is significant with delivery out to two years or more, my estimate. Obviously if you track down a used Zstage then no long wait. You could have it re-certified by Decware as well which also renews the unlimited warranty. Give Steve a call at Decware for details. The Zstage will provide up to 5 Volts gain, versus typical sources and preamps which are at 2 Volts. So it is an option. I do not own a Zstage but from the info on Decware’s website I get the impression a typical Zstage user wants additional gain and the ability to tailor the sound with various 12AU7 tubes. I’d also discuss with Stev tube availability from Decware, as well as alternate tube options.
You probably have found the manual, but if not here is a link:
Here is the Product Info page: