Yes Systembuilder, as 4est stated, it is done frequently. It's a great way to eliminate the need for extra ICs and keep the signal into the main speakers as "pure" as possible rather than running the entire signal through a crossover system first.
All you need to know is the input impedance (resistance) of the amplifier and your desired HP Filter frequency and you can calculate the capacitor value:
C = 1 / (2 * pi * F * R)
All you need to know is the input impedance (resistance) of the amplifier and your desired HP Filter frequency and you can calculate the capacitor value:
C = 1 / (2 * pi * F * R)