I would like to squeak better bass performance from the KEFs and a warmer or lusher mid might be good with the otherwise very neutral MyTek.
I don’t know about the Gryphon Diablo 120 but have the Luxman L-590AXII. Just like Fatdaddy2, the Luxman replaced a costlier separates in my main system. The separates are now relegated to the secondary system which i rarely use.
Perhaps owners of the Gryphon Diablo 120 might be able to explain on the sonic attributes of the amp. I find the L-590AXII to be a neutral sounding amp with very little coloration. It won’t give you a big ballsy bass. What you get is a clean sounding bass which is taut and defined. You will hear all the layering and texture in the bass if it’s in the recording. Other amps might mask this layered or textured bass a little with the bass sounding smeared. In other words, the bass with other amps might sound fuller, bigger or ballsier while with the Luxman you get a leaner and cleaner bass but one that’s textured and detailed. The dynamics, punch and kick in the midbass and upper bass are all present in the Luxman but you just get a clean bass as opposed to boom boom bass with other amps which may sound more impressive or worse depending on musical preference.
Midrange is also very clean, perhaps leaning very slightly to warm. Treble is airy and detailed with a slight tube-like glow which is very nice. I use a quality(rather costly) power cord on the Luxman and the source is also quite decent.
I believe both Gryphon and Luxman are good amps and the choice will be dependent on system matching and listening preference. Good luck.