The underlying assumption you imply is that high powered solid state has a sound - well that's not true, its going to be speaker dependent.
I find the main 'sound' of most transistor amps the is the slight presence of odd-ordered harmonics, which manifests to the human ear as 'brightness'. The human ear is more sensitive to odd ordered harmonics than just about anything else due to the fact that it uses them to determine how loud a sound is. However I do agree that not all speakers work with all amps and there is indeed a speaker dependency! For more on that see http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php
My point was that you need an amp that is driving the speakers properly and with over 20 years experience with Tannoy 15" drivers in various cabinets, I do believe that many folk incorrectly assume that you only need a few watts because of the high efficiency.
Agreed. I regard the Tannoy has being moderate efficiency rather than high efficiency. You need some wattage.
I believe that controlling the 15" driver, which has been specifically designed to be phase coherent through the crossover point at 1k, is paramount to maintaining that design intent.
For this you don't need high power- you need good bass extension out of the amp. In fact the driver in the Tannoy seems to be happier if the amp has a lower damping factor rather than higher, typical of a lot of speakers with efficiencies in the upper 90s or higher. My speakers are 98 db with dual 15" drivers, yet they are easily 'controlled' by a 5-watt amp, even if that 5 watts is really not enough power to satisfy.