Gryphon and Vitus are both great amps. I demoed both the Diablo 300 and the RI-101 and liked the RI-101 since it was a bit more organic and fit the sounds signature I have been looking for for a while. The Diablo was great, just felt that it sounded a bit harsh on some songs. If I was to guess it was from the preamp side not the amp. I felt the RI-101 combined the full body sound like tube, with clear/crisp highs, and tight controlled bass. I have never heard anything quite like it. I can only imagine how good the SIA-30 is.
If you like more forward vocals then you may like the Diablos better. It’s a total personal preference.