Home Cinema Speaker Cable Question

Hello,
My Dad recently bought a Panasonic BT200 home cinema system which i fitted for him. However he also had a set of 4 speakers which he had connected to a satalite reciever with built in amp before and had existing cables in place. I removed the existing speaker but the only thing is that the existing cables are just a generic five core cable which he used two of the five wires. Currently the cables are behind the wallpaper and have left them in place, these cables happen to be even thinner than the already thin cables that came with the system. As he didnt want to remove the originals i cut the new ones down (the were not long enough) which have there own colour coded plugs and soldered them to the existing one. Problem is the system doesnt sound good at all, if anything the speakers sound weak. So would you recommend replacing all the cables with single length speaker cables with the same thickness as the one supplied, would i get away with using 1.0mm 96 strand speaker cable? also what is the best method of joing two wires as i dont think i will be able to remove the cables from the plugs

I would say electrical tape.

well dont the qauge of speaker wires, make a little difference?? 1mm is extremely tinny.

ye prob not.