Bi-amp with 5ch amp, any hook up suggestions?

I have a Chiro C-500 amp that I wish to use in a bi-amp application and was wondering what you good folks have done for the interconnect between the pre/pro and amp. I am considering a few options and would like to know what you think, all suggestions welcome.

0) Monster Y-cable
1) Build a Y-cable from quality parts, splitting near the pre/pro, or could split near the amp.
2) Open the amp and somehow connect pairs of inputs
3) Open the Pre/pro to add another set of RCAs and run to ICs
4) Try to use the other outputs on the Chiro not used, rewire to feed as front channels in CD/stereo bypass mode.

Also wondering if not having the 5th channel driven will in any way affet performance?

Any suggestions? Looking for easiest and best sounding solutions. Thanks much!
do not touch pre/pro and get things with y-connector since you will make the units to loose its values and most-definitely use HT-bypass mode if possible.

you can get WBT or Cardas as well depending on how much you're willing to spend.

in any case any unused channel might on might not affect the performance depending on how your amp is built i.e. its quality. 5th channel thereafter can be used for swinging a subwoofer.
I have a Theta Dreadnaught 5 channel amp that I use to biamp my Maggie 3.6R's, leaving one channel unused.
It does make a nice improvement to the 3.6's being biamped;
I made up the 'Y' connection myself.
The unused channel appears not to have been frazzled from this arrangement.
Marakanetz is right. Don't modify the preamp. I would use a y-connector and split at the amp side. It saves you an expensive interconnect.
Quest for Sound also has a "phoenix pro 418" solid y-connector which I like or I agree with a quality y-cable as above.