We also need to know what speaker make and model you have or are considering.  I have nothing against monoblock amps but bi-amping in most situations is a waste of money.  The bulk of the power goes to the woofer or mid-woofer, so adding a separate amp for the tweeter, which uses very little relative power, usually has little benefit.  Most speaker manufacturers add a second set of binding posts (speaker terminals) just as a selling point for marketing purposes.  Few speakers really benefit from bi-amping.  You would gain more by putting the money into two really good monoblock amps or a stereo amp and put your savings into the speakers which are the most important part in determining the sound quality you will get.