PIONEER S-DV55SW-K + BASH S300

Hi,
I have PIONEER S-DV55SW-K and BASH S300 both believe to be very trust worthy.
Enjoined many years Pioneer 5.1 system, and now it is time to marry these two, so I can continue enjoin
very good SubWoofer with my new Yamaha 7.1 receiver. Problem is my total inexperience with this.
Pioneer DV55 Sub is 65W / 8 Ohm, and Bash S300 is 300W /4 Ohm.
Figured out that Amp has to be out of the Sub. Original Pioneer amp will have to stay in.
Please help me make this work since this box dimension is the only one that fit the space available.