Well, I'll take stab. The B&W 685 is an excellent bookshelf loudspeaker for the price. Good choice. While I don't have the 685s, I do have the 683s so at least in we're in the same family. First yes to bi-wiring for sure. I would do that for mimimizing distortion and separating the lower and higher reproduced frequencies being fed to the 685's. Second, since B&Ws can take the power and like to be driven, a solid conductor core of at least 14 AWG(copper with at least a small percentage of silver) in a speaker cable would be a good recommendation. I do believe that solid is superior to stranded so in light of that, take a look at Audioquest. AQ is frequently sold by dealers who also sell B&W. Depending on your budget and how many feet of cable you need, AQ offers a good selection and variety in a wide price range. They sell both prepared and unterminated cables. You may simply want to visit your closest AQ dealer and get their recommendation. They probobaly have speaker cable on reels available at any length you need. So again, 14 AWG min, solid copper conductor with some silver, etc. would be my recommendation. There are hundreds of choices but keep it simple.
