I finally see what you want to do, and you can't really do it. Here's why.
When you bi-amp speakers using a run-of-the-mill receiver like the 573, there is no "crossing over" happening in the receiver. The receiver outputs the full frequency over both bi-amped channels to each speaker. Any crossing over is performed inside the speaker.
Now, if you don't connect a subwoofer to a 5.1 receiver, it will just output the .1 low frequencies to the front speakers. However, as I wrote above, even if you bi-amped the speakers, those low frequencies will go to the tweeter/midrange driver too. So you're not getting the total separation that you would by sending the .1 to a dedicated powered subwoofer.
A pair of speakers with woofers (10" or 12", or even 8") can still produce lots of bass, even if it's not the exact ".1" idea that you're looking for. If you intend to drive large speakers though, you might consider a receiver with more power than the 573.