is biamping speakers good idea?

Have just bought ploneer m72 amp and c72 preamp , with pioneer pd65 cd can I biamp using m72?
Hello Musicman,
Which speakers are you using?
what do you mean biamp using m72? Are you talking about adding another amp...or do you mean bi-wire?
you can but to get the most benefit of bi-amping, you'll need an active crossover that goes between the preamp and amps. i use a first watt b4 crossover for that purposes. it also requires a lot of listening to dial in the XO to get it just right (a lot of listening is not a bad thing!).

bi-wiring doesn't have much benefit.

It's not as easy as it sounds. You have to get everything just right in regard to matching the two amps, and I was never successful.
^^^ generally true. If your amps for the highs/mids are not the same as the amps for the lows, you'll need an active XO with sufficient adjustment to get the levels from the amps set up properly for seamless FR. This usually meanings some measuring equipment or software like TrueRTA and the like.
Biamping, as I understand it, means using your amp twice a year.