Thanks Blitz17 and magnox for the advice. I called them pine sheets but I suppose they are boards, although two foot wide. I am also originally from the UK as well and I never saw such big boards before over there, but here they seem to be everywhere, but plywood I still have yet to find (it is a bit like learning to walk again moving to a new place

). I am not sure if the pine is kiln-dried although they look really good quality and are only about 15 euros each (for this area that is cheap).
The lightness of the pine and ease to work with is quite appealing, although the robustness of the ply (if I can find it!) seems wise. My carpentry skills are very basic so think I might tackle the backbox first in pine to get some practice in, and try to locate some ply for the cabinet (as it is going to be large). My other limitations are I only have a few tools here so need to get some more. I have a jigsaw, handsaw, and a decent electric screwdriver and drill.
Could just check one more thing - how do you make those perfect holes for a speaker and dmd in the front of the backglass box? I have woodglue, long steel-rule, and need to get G-clamps, etc. Also if you can advise any other essential electric tools, etc. then that would be a big help.
Many thanks again,
Vic