Ejlif's advice should be followed.Replacing your amp will change the sound but it cannot do anything to correct the weaknesses of your preamp and cd player.
Your room is large and as Raquel stated your speakers just may not be up to filling the room with the sound you are looking for.Further do you use a M.C. cartridge and if you do what is the output.
Your room is large and as Raquel stated your speakers just may not be up to filling the room with the sound you are looking for.Further do you use a M.C. cartridge and if you do what is the output.