George, are you sure that TubeGuru amp actually has a 4 ohm tap?Hi Al, yes when I Googled those amps one of the forum/reviews? said to use the 4ohm tap for hard to drive speakers. And the feedback is adjustable from 0 to some 30db That’s what led me to think so.
I did the same on my 805 sets and zero fb had soft ill defined bass, nice mids/and not much sparkle on the highs of the Monolithiths. Max 35db fb tightened the bass considerably and gave more (still not enough)sparkle in the highs (1ohm load) ouch!!.
In the end I went big bi-amp solid state, as 50w set was not enough for loud level transients, but then the Monoliths are only around 86db where the OP’s Kefs are a touch higher and not as bad loading, as the Monoliths have far worse negative phase angles at 3 points with low impedance’s.
BTW: Edgar Kramer (reviewer) of Australian HiFi/ 6Moons/ and Audio Esoterica had a pair of (Elson Silva) Cymer Southern Star SE35, 35w single 13E1, set monoblocks and his drove his Wilson Watt 8’s comfortably, but in the end weren’t enough when the crew came around and wanted it turned up more than he does.
http://www.6moons.com/audioreviews/cymer/3.html
Cheers George