Biwiring Mani-2's...

If I'm connecting a plinius 9200 to mani-2's, do I need biwire cables?

If I don't, can anyone summarize why I might still want to buy them even though I have no intention of getting a different amp?
Bi-wire and Bi-amp are 2 different things. Bi-wire is when you connect 1 amp to both sets of posts on the speaker and bi-amp is when you have 2 separate amps for the same speaker. From some of the recent posts here it seems as if bi-wiring causes a loss in the bass. That being said I had bi-wired my mission/cyrus 782's and it increased the bass but just slightly. It may have been my cable. It was musicline from signet where there were 2 separate runs of cable (stranded). It had 24 wires for the bass section and 104 for the high end. Both high and low runs equaled the same gauge.

So back to your question which is bi-wiring. Either just use the jumpers or get a bi-wire cable (but again from some recent posts you may loose a little bass with bi-wiring). Also with bi-wiring you do bypass the crossover which may explain why some folks loose some bass.
i used to bi-wire my mani's with 2 pairs of dimarzio speaker cables: both terminated at the amp, and 1 pair to each the tweeter and woofer. i have since upgraded my cables and have gone the speaker jumper route instead of bi-wire.
Also with bi-wiring you do bypass the crossover . . .
I'm not an authority, but I'm pretty sure this is untrue in most cases. In bi-wireable speakers the woofer has a low-pass filter, and the Mid/Tweeter has a hi-pass filter that also divides frequencies between the mid and tweeter drivers (in 3 way designs).

I have tried multiple cables on my Mani's as well as other speakers and have never noticed a loss in bass. I settled on a set of Totem Bi-Wire cables for mine which are the best I've used.