you really, really need to search the archives on biamping. There is one thread on this topic that has some excellent discussion and contribution from Steve McCormack. Find it, read it.
Also, I did biamp my Mani's. The result was at best a marginal improvement. I corresponded with Totem and they indicate you're much better off using a single higher power amp than biamping - so with the Manis the bang for the buck in adding a second amp is ver marginal. Not so with other speakers, but true for Manis. That said, since you have the second amp already - get some Y adapters (they are cheap) and try it. Just do it and you will have your questions answered.
Also, I did biamp my Mani's. The result was at best a marginal improvement. I corresponded with Totem and they indicate you're much better off using a single higher power amp than biamping - so with the Manis the bang for the buck in adding a second amp is ver marginal. Not so with other speakers, but true for Manis. That said, since you have the second amp already - get some Y adapters (they are cheap) and try it. Just do it and you will have your questions answered.