I heard them once. They are compact and very well-built, but didn't sound particularly "tubey" to me. While most audiophiles will automatically say they want an amp that sounds neutral, IMO, when someone wants tubes, they want it to sound like tubes - for better or worse.
Put it this way - the Octave did not sound nearly as "beautiful," for lack of a better word, as my Viva. I also owned a Mastersound at one point, which I thought was very neutral-sounding. Some refer to it as "colorless".
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