@james633 , You have exactly the right approach. All systems using subwoofer miss more than 1/2 the benefit by not using a high pass filter on the main speakers. It can be as simple as adding a series capacitor to the input of your amp. You just have to know the input impedance of the amplifier. f = 1/2piRC or C = 1/2piRf. R is in ohms and C is in Farads so you have to convert to micro and picofarads. Order the right cap from Digikey. They might cost you $10 at most.
Next you can get either an analog or digital 2 way crossover and bypass whatever comes in the subwoofer. I like 12 dB/octave in analog crossovers. I use 48 dB/octave digital.
Next you can get either an analog or digital 2 way crossover and bypass whatever comes in the subwoofer. I like 12 dB/octave in analog crossovers. I use 48 dB/octave digital.