mono blocks or true bi amping,

wanted to know if some one here knew about true bi amping.Is it better to use four mono blocks for two speakers, or can i get the same sound using one amp for the highs and one for the lows. or just keep the one intire chanel to one speaker as if i was using true mono blocks.
It would help to know which amps/which speakers??In many cases less is more.
the parasound halo A21 and a set of b&w dm640 series which are 4 ohms spreakers