Are B&W Nautilus 803's stock copper wire jumpers good?

I believe that the benefits of bi-wiring can only be heard when the wire for each termination of the speaker comes directly from the amplifier. I would recommend you audition a high quality pre-terminated bi-wire run--especially if you are listening to N803s. You've got about 50% of your speaker's capabilities hidden right now if you are using jumpers. I own a pair of N804s and I feel that bi-wiring is essential. Perhaps others could give you a first hand account of how they wired their N803s.

By all means invest the bucks in bi-wire cables. I am running 803's now with a Sonic Frontiers Power 2 amp and MIT cables. While the combo sounded good using a non bi-wire cable and the B&W Jumpers, the speakers came to life when I changed to the MIT cables.