I too had a similar experience with the Rogue Cronus Magnum ii. I am, by no means, an expert and I am only relaying my impressions. This was probably 5 yeas ago and the Cronus was my third step of upgrades with tube gear and I was really let down by its lack of “tube sound”. I now have all separate tube gear in my analog chain (phono preamp, line preamp and SET monoblock power amps. Ironically, I too have the same Cambridge Audio Azur that I use only as my DAC while streaming).
I am surprised no one has mentioned what I consider to be the single greatest factor to why the Cronus lacks what I call the tube sound. This being that it has solid state rectification. I know that some people actually like this and Rogue markets it as one of the benefits in some of their models. All of the pieces in my current chain have tube rectification. To me this has been the real key to getting more tube sound. I have had two experiences with tube gear that use a solid state rectifier, the Cronus and the Cary Audio SLI-80HS*. Both the Rogue and the Cary lacked the warmth and space I was seeking. And, like a few have mentioned here, I went down the rabbit hole with both the Cary and the Rogue trying countless NOS tube combinations and spending gobs of money. Fortunately, I have been able to use some of those tubes, with great results, in subsequent tube gear. Also, I have had a couple Cary pieces since this one that use tube rectification and have loved them (including my current phono preamp, the Cary PH302-MKII).
Again, this is personal preference and many people actually prefer what the combo of solid state rectification and tubes offer. Just not me. I want tubes to sound like tubes.
Hope this helps.
Jared
*interestingly enough, I read about a year ago that Rogue was suing Cary over the use of solid state rectification in tube amplifiers claiming they stole a design. Haven’t heard whether or not it was settled.