bi-amping will help but do you need that help? Why do you want to bi-amp?
Are you able to play loud enough with the current power? If yes, than you probably do not need more amplification. To have enough power to play at a loud level, and head room for another 10db for dynamics in the music. I am sure you won't want to watch a movie at too loud a level. Though you may like your music to be loud once in a while.
Calculate your power requirements here -
http://www.crownaudio.com/apps_htm/designtools/elect-pwr-req.htm
bi-amping one channel to tweeters and another to array of woofers is not much of a help as tweeters consume much less power. It would only help if you could power each woofer separately. Not sure if passive crossover in your speakers would allow that. See this link -
http://sound.westhost.com/bi-amp.htm#basics it says for any useful bi-amping, you need to disconnect your passive crossover. I am sure you don't want to do that!
It would make a lot of sense if somehow power from two different channels gets summed up, and go to your speaker on a single wire. I think Onkyo *claims* it can be done on some of its models - 2 rear channels get useless in this mode and their power gets summed up in the fronts.
Another way to bi-amp is - have different amplifiers for each speaker. You may buy single channel amps, or multiple stereo amps that can be bridged. 354 has a pre-out.
I was in exactly similar state of mind as you, but above is what I have learnt in last few months. I am a newbie too
regards
So is bi-amping really useless for my setup?
Thanks