I found the Octave to be a bit more mellow than other DACs I have. With a mellow tube amp it was too much and the system I felt needed more cowbell. However, I liked the Octave with the 009s for this reason. On the other hand, my regular DAC, the Reference 7.1 had a bit too strong bass for use with the same tubes and the Octave was a better match in that regard.
The Octave, when brand new, sounds different to how it is after the electronics settle down (I hate saying "burn-in"). At first, everything sounds like it has drunk half-a-dozen cans of Red Bull first. I think people end up selling them because they get used to this crazy, energised sound then lose interest after that changes to the final, more mellow presentation.