Replacing stock jumpers make a significant improvement. Best to use same wire as main speaker wire if possible but many companies make quality jumpers ie nordost. There is also a belief that rather than running a bi wire set run a quality main set and the jumpers to the other set of speaker terminals- nordost now believes this provides better sound. I was running a bi wire set to my b&w 800d and are now running nordost Valhalla single run with Valhalla jumpers to the other terminal set. The stock jumpers provided with many speakers are junk.
