I recently bought a Integra DTR-70.1 a/v reciever and i have the option of 4ohm or 6ohm. 6ohm include 6 to 15ohm impedance speaker. So i have a pair of M80 from and VP150 center so is there any problem to set my speaker to 4ohm or should i stick with the option 6ohm ?

Also, this amplifier can be bi-amped, does it really affect something for stereo listening to my M80, anyone has notice an improvement ?

Thanks

Nad C356 DAC & C515
Axiom M3v3
Grant Fidelity RPF-120 MKII
Analysis Plus Black Oval 12&10
JRiver 19