Binger,
On the face of it, it certainly sounds like a tiny short, either with a stray strand of wire between the terminals of perhaps a short (rare) in one of the speakers themselves.
By the way, the 6-ohm VP150 is an easy load for any AV receiver. Does your Yamaha have an impedance switch or setting on the rear panel? It should be at the highest setting--8 ohms. If it's at a lower setting, that will impose a current/voltage restriction on the power supply, dramatically reducing the output power and could be causing the shut-down.
As some have noted, individual swapping out of the speakers and cables might reveal the source of the short.
But check the impedance switch first, if there is one.
Regards,
Alan
