woohoo, sorted it!
i tried using both pairs as stav suggested and got sound, but it gave me a horrible grasshopper like buzzing through the tweeters, so thought maybe the speakers were duff, i faded the fronts back in, noticed the fronts had the buzzing too, i disconected the rears and the buzzing stopped, so connecting all 4 were giving me the buzz, in the end i cut my losses and ran new speaker wires through the car direct too the head unit leaving the lexus wires out all together, strange stuff eh!