connecting sub to integrated with no rca out

i have a little dared tube/mosfet hybrid(precursor of fatman itube} bookshelves with 13wpc but not a sub out or any rca out. am using fostex 126 bookshelves with a little 8" sub that has all desired connections. what do you suggest as hookup options for this combo? i am concerned that running the speaker cable in to the sub and then out to the speakers will add sub electronics to the path that will spoil the speaker amp synergy.