Having just auditioned Vitus RS-101, RI-101 and the Gryphon Diablo (plus Pass 250.8) I have to agree totally with the reviewers above. The Vitus is much more refined than the Diablo and does not impart as much of its own character to the music (particularly midrange).
I tested both with the pre amps and without, given I noted a distortion in the Diablo with some music (mainly trumpets). So I also used my Chord Dave as preamp which solved that issue and gave a much clearer sound.
In the end I went with the RS-101 rather than the RI-101. Literature and reviews say they have the same amp construction, but not according to Hans-Ole. The RS has a "stronger PSU....to provide better drive for difficult loads". He believes it does not change the sound, but I found it quite a bit better than the RI-101. Best to try both.