powered sub to an Adcom speaker selector box

I have an Adcom 5400 amp with a Adcom GTP 350 preamp . The amp is connected to an Adcom 3 speaker selector. I also have a Kilpsch  R-100SW as my subwoofer. Can I hook the subwoofer directly to the speaker box like a regular speaker and turn the low pass to around 80hz.  The other two sets of speaker are 901s. I can't find it anywhere but it seems as feasible as wiring the subwoofer in line with one of the speakers as many do. The speaker selector is passive.