I have been listening to Tannoy GRF Pro's and 15" Monitor Golds in Canterbury sized cabinets for over 15 years. In my view tubes are not the way to go - I've had Futterman OTL's, Quicksilvers, Conrads, EAR etc high power, low power , pentode, triode, ultralinear 6550's, EL34's, 8417's, 211's etc. The ear opening experience I had was listening to von Karajan's Beethoven 5th on the GRF Pro's with 500 watts of heavily modified Perreaux 5150B - as in the only thing original was the power supply and mosfets. Even though the speakers are hugely efficient the big power amp's headroom and control over the speakers clearly enabled the relentlessness of this performance to be communicated which I never previously heard. My supposition is that high power amps provide better control over the driver, Tannoys own reference amplifier was a 250wpc mosfet amp. I have come to the view that if you value speed and timing high current solid state is the way to go, I use a 50watt high current ss amp. I would look at something like MBL's or Pass Labs.
I would also echo the views above, speaker positioning and angling adjustments of even 1/2 an inch can yield significant changes in openness, balance and bottom end.