Thanks Beranrose for your response.
The main concentric driver on the D900 comes in at about my head height when sitting down so I don't have the same problem. The D700 is a few inches shorter than the D900 so I can see where the problem is coming from. My first instict would be to try and find some stands to increase the height of the speakers, but I could be wrong. Best experiment a bit and see what works.
I kept my previous ESS AMT Monitors for the two back speakers, along with the SAE Two A14 amplifier that used to be my main system starting 25 years ago. These are completely unmatched with the Tannoys, so I reduced their high range a bit and keep the volume lower than the Tannoys. I would love to use a pair of D500s or D700s at the back but could not justify the cost at the time. Now the newer models are much more expensive. The SAE amplifier blew up recently and I had to use a junk Pioneer amplifier for a while. This is how I know that the rear channels are not that critical for amplifier quality.
Since December I have been working up a biamplification system for the Tannoys using a Behringer DCX 2496 digital crossover and a second Musical Fidelity A308CR amplifier. It works extremely well but have not yet managed a good solution for a post crossover volume control (I have to adjust two different controls together). The Tannoys seem to come alive with bi-amplification so I will persevere. The expense of this experiment, which also involves a solution for DVD-A and SACD playback has delayed other aspects of the system.
The centre channel has stumped me so far. I had hoped to pick up a D750 but missed out on this. Unlike the rear channels, the centre has to match the front channels properly. I tried one of the ESS speakers and also a Tannoy Saturn speaker. Neither worked. (A borrowed D500 worked well.) For now I have moved the two front speakers slightly closer together and this seems to work OK. I have to sort the bi-amplification before I spend more money on anything else. Incedentally the Behringer has enough channels to bi-amplify the centre once I finally get it.
I am reluctant to make recommendations as I tend to go out and see whats available once every ten or fifteen years but don't constantly stay in touch. I have been very happy with Musical Fidelity amplifiers, preamps, and CD players, both 3.2 and 308. I also use a A3 24 DAC to play music from my PC. I spent enough money at a nearby hifi place that they don't mind letting me audition equipment for extended periods. The one piece of equipment that really made a difference for me is an Arcam FMJ AV8 (multichannel preamp). Beyond the budget for now.
I am indeed fortunate that my wife understands that music is important to me and is willing to go the extra mile. I fitted curtain rails close to the ceiling on three sides of the living room. One side does actually cover large windows. The other two unlined sections can be drawn into the corners where they are relatively unobtrusive. Even when drawn into the corners they do make a difference to the sound. No-one quibbles about the appearance once they hear the difference the curtains make.
Hope this is of some value.