That Yamaha receiver can drive the VP180 without any problem. The part about it having only 8ohm and 6ohm setting it just a null setting inside the system. it really doens't make any difference one way or the other.
The power supply inside the unit can run a 4ohm speaker. Just not at maximum volume for a constant time. So don't turn the volume all the way up.
Axiom: ADA1000, LFR1100, VP180, QS8, EP500, M3, M3comp
AudioSource: Amp One/A