The crown just a normal power amp, with a " flat" freq. response.
I think I will prefer the 20/20 because I have a lot of low end form my cab ( Marshall 2888 with greenback) and the triaxis can deliver probably more then i will ever need. If I even want more bass, I'm gonna switch back to the crown and sell back the 20/20.
The Crown is a HiFi amp and not a good partner for a tube preamp. It's not a tube amp for starters - that means you have to be careful about cooking the input. The Triaxis has a very hot output. With a tube poweramp you can push the input pretty hard without cooking it. HiFi amps have, as you say, a flatter frequency response and a wide frequency range. A guitar power amp is more targeted to the frequencies that guitars use. It is more biased towards lows and mids. a HiFi amp will go both lower and higher than a guitar power amp. You can look at a guitar power amp as being better "tuned" to the Triaxis than a HiFi amp.
You have already tried the Triaxis with the Crown and you didn't like it. Why would you consider it again as an option? The 20/20 is a nice amp, but it can be a little thin sounding - depending on the music you play.