Specs for replacing woofers?

[pmc]

Not directly a jukebox/arcade question but I know you guys know the answer to this. 

I have an old set of Infinity RS-2001 bookshelves. One of the woofers is torn and sounds like heck. Infinity will sell me a new woofer for $40 plus shipping, but I figured I could probably replace woofers in both speakers with a Parts Express woofer cheaper and not dramatically impact sound quality (maybe even improve it?).

What specs do I need to match up? I know that the power rating and impedance need to match, but what about the crossover?

The RS-2001 uses a 6.5" 6-ohm woofer with a freq-response of 55Hz-22kHz. The crossover is at 4.8kHz. Power rating is 15-75W and sensitivity is 89dB.

I'm sure that most any 6-ohm woofer that falls under 75W could do fine, but is that all I need to worry about?

Is this course of action inadvisable?

Thanks in advance!

-pmc