That would actually get me some use out of the "redundant" components. But would it work?
Bi-amping itself, is redundant.
You have to realize that the surround channels use the same power supply. So this receiver is rated 60w(8ohm)/120w(4ohm) but when you simply don't use anything but the two main channels, you get closer to 100w(8ohm)/200w (4ohm) thanks to the robust power supply designed for multiple channels.
the crossover on the sub will take care of its frequencies, and they think sending the full signal to my speakers (old low-end Paradigm towers) will produce a better overall mix anyway.
That's got me a little confused--I thought bass management was my #1 issue.
I can see where they're coming from... In the bass frequencies (especially ~40hz - 120hz), a single omnipolar source will cause lots of peaks and dips in the frequency response. Adding a second will smooth that out greatly. Adding a third (a sub) will further smooth that out and over multiple seats too. Ideally you want three, even four subwoofers rather than just one.
The problem is that without a method of setting proper delays and levels, you won't be able to set up the sub properly, and your power handling will be limited by the main speakers rather than by the much more powerful subwoofer. If the sub is receiving the signal late (which is very possible given its internal circuitry) or early (which is also possible) then it could really muddy things up.
I believe strongly in bass management. There`s some select scenarios where I feel running mains full range can be great, especially if your mains are sealed and designed for high power handling, like these Geddes speakers.
Abbey
I feel vented speakers can`t handle tones below their Fb so it`s not recommended.