I used to use Nordost Solar Wind bi-wire when i had my 803's.I think in general, Nordost cables work well with B&W.There is much debate as to how much difference different speaker cables make, but for the 803's you need a cable able to keep the bass under control.Possibly decent gauge £3/m copper wire for the bass drivers and depending on the balance of your system you might want silver wire for the mid/high frequency drivers.
I currently use Ps audio xtreme statement bi-wire cables.
They use heavy gauge copper for the bass and silver plated copper for the highs