Thanks Jon Boy, I did try to figure it all out beforehand but still came across problems i.e. one thing I got a bit wrong was the length of the cables I would need, I have got away with it but only just, but going round corners under floors & back up eats cable length
Mr Gobby, thanks for your comments, the height from the floor to the bottom of the screen (not speaker) is 93cm, this was supposed to be 86cm but I have had to lift the screen to get the undermounted speaker in because I could not go with my original plan of having side speakers hidden behind the screen firing sideways. We find the height ok, my eyes are about quarter the way up the screen.
I left the wall as blockwork, it does not show so would have been a waste of money plus the mount brings the tv forward of the woodwork for heat dispersal.
I wanted the DVD & Amps to look as though they were floating in the 'fire hole' so I built a rack using metal shelving & brackets but to be honest I am not happy with the outcome, I might build another one with glass shelves. I have put Ikea Trettion lights at the back of each shelf to enhance the floating effect (hard to photograph those lights) as well as behind the top of the plasma and some LED spots on the side of the chimney firing into the corners all controlled with a £16 unit from Aldi
Nige