Speaker cable change?...not necessarily...unless it just doesn't sound so good in the first place, then you can change of course. As for Balanced making an improvement, yes it probably might, even though your sources are not balanced. All you have to do is pick up some very good high end balanced desing on the net hear and try it!...then you'll know. Then all you have to do is sell what you don't like...easy enough.
good luck
good luck