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

Howdy,
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!