how to connect a passive sub to my av reciever

hi people have a onkyo txsr606 but have a passive sub which wont connect i think i need to do it through a amp would a
ACOUSTIC SOLUTIONS sp101 be upto the job having to buy second hand stuff so any other suggestions would be very greatfull
One idea;

Sub out (via RCA or XLR) from pre-pro or AVR ---->(RCA or XLR input on) the Subwoofer Amp, then Subwoofer amp out (via speaker cable) ----> (via speaker cable) Passive Subwoofer in.
When you say passive sub, I believe you mean unpowered. I would say connect your sub through a dedicated 1-channel sub amp like an NHT MA-1. I have 2 for sale.
If your Onkyo has a "B" set of speakers posts then connect the sub to the "B" binding posts. That will send the full range to the sub and set the passive sub's crossover manually as you will get the full range from there. If you have zone2 it is the same as B set of speakers.