possible upgrade to biwire speakers

The real gain is to go active. Bi-wire is no different than using a heavier gauge wire—the back EMF returns to the same single amp driving the entire bandwidth and dealing with the multiple impedance curves of two or more drivers. Bi-amping may provide some benefit, but not to the extent as using an active crossover and an amp for each driver.

If you're interested in more in-depth technical explanations, read these:

http://www.tnt-audio.com/casse/active_speakers_intro1_e.html
http://sound.westhost.com/biamp-vs-passive.htm#2.2

As suggested above, biwireable speakers don't necessarily guarantee better sound and shouldn't be considered as a feature when shopping for speakers. Also, non-biwireable speakers allow the use of a single run of high-quality speaker cable which will cost significantly less than a similiar cable of bi-wire configuration. There are many quality high-end speakers today which are not bi-wireable.

the ability to bi-wire is not really an assurance of better sound. the psb's are solid speakers, but an upgrade within the psb line, or going with a totem one, or another like monitor, will make a difference.

If you biamp then you can make a modest improvement but I don't think this warrents being your main consideration in up-grading your speakers.