parts-express has some speaker level high pass crossover can put in-line to the main speaker to
filter
out the low
frequency
http://www.parts-express.com/100-hz-high-pass-8-ohm-crossover--266-462?utm_source=google&utm_med...
you can lowering the crossover frequency to 50-60 Hz by increase the capacitor value (add a 100-150uf capacitor parallel to the existing one),
Than you can use the Integrated Amp pre-out to connect to your sub-woofer line-in.
http://www.parts-express.com/100-hz-high-pass-8-ohm-crossover--266-462?utm_source=google&utm_med...
you can lowering the crossover frequency to 50-60 Hz by increase the capacitor value (add a 100-150uf capacitor parallel to the existing one),
Than you can use the Integrated Amp pre-out to connect to your sub-woofer line-in.