My pleasure.I think the absolute sweet-spot would be to move the piano, have the TV in the centre of that, with speakers either side, then spin the armchair round 180 degrees and move to the back wall (obviously I'd have to persuade the dog that it is no longer his armchair and find somewhere else for the piano (neither of which may go down well ;-))). I hadn't considered speakers either side of the piano. May work, but there's a radiator immediately to the left of the piano, and a dry line wall perpendicular to the right side so the RH speaker would be right in a corner.
I had thought about option two, but was concerned that the TV would then block access to opening the window. I may well give that a go though, thanks for the suggestions.
Well, my plan was not to move the TV. The left speaker to the left of the TV (if room enough) and the right speaker slightly closer towards the TV. Might work.