SoX doesn’t have a JACK driver. It wouldn’t be too difficult to write one, but due to the architecture of SoX, the latency would always be higher than strictly necessary.
If all you need is simple IIR filtering, just use a LADSPA host such as JACK Rack and suitable plugins, such as those by Matthias Nagorni or buttlow_iir
/butthigh_iir
etc. from Steve Harris’s collection.