You better put them in series, 12 ohms would be a better value for the output amplifier of the passive. The value is also closer to the 8 ohms the passive is expecting.
Wiring in cable as monster is always better, especially if you have long distances. You will not loose any power on your speaker cords. But try to keep every wire from both channels in a equal length especially if your putting them in series. Dont forget also the serial connection between all the speakers, keep them equal.
I myself are using Kimber speaker cable for the connection (from Russ Andrews) wired to B&W ceiling speakers.
Yes, I kown my spelling is horrible…