I recently purchased the Yamaha RX-V559 Receiver to act as the hub of all my equipment and realized that I couldn't hook up my passive subwoofer because there is only a speaker jack for an active sub. (no slot for a two wire sub woofer speaker input)

Is there any way I can avoid going out and buying a new active sub/use my existing kit?

Yes - use a mono or stereo basic amp hooked up to the sub out RCA connectors.

There are good sites that offer used units.

thanks. I did some searches for a basic amp and everything that comes up seems overkill for my simple application. Do you have an example of what you meant?

well, if your sub has a crossover )probably not though) you can hook it up through the B speakers and that will get you bass. however, not LFE as it is intended