If the STF-1 is like my PSB, the speaker connections only keep the higher frequencies from the sub, in my case 80hz and above, but pass a full range signal through to the speakers. So, the speakers still receive a full range signal. Not the prefered method, but there if it is your only option. Hsu does make filters you can use to bypass this, and you can select the filter settings when ordering. It's $100 I think.
Ed
* Sierra-2EX's W/V2 crossover upgrade
* (2) Rythmik F12's
* Parasound Halo P6
* Audio by Van Alstine DVA-M225 Monoblock Amps
* MiniDSP 2x4HD For Sub calibration
*World's Best Cables Canare 4S11 speaker cables