Yamaha receivers are much more bulletproof than other manufacturers and are more than capable of the 4 ohm load. As oex said no one is going to guarantee it to you though. With the discrete codes available, the YPAO, and the stability of the Yamaha product I would also suggest their receivers. With the Yamaha receivers you can purposely short out the speaker wires and you will not hurt anything. The receiver will shut off and once you turn it back on it will tell you to "check speaker wire" . Try this with most of the other brands out there, especially Sony or Pioneer...

I say get the Yamaha. You'll be satisfied for years. Make sure to get a model or two above what you think you need for future upgrade options.

Also like oex said, one nice piece at a time can be built into a GREAT system where as compromises must be made to purchase a whole system at one time.