I have a mid-level Elite (4 year old model) and others have said that it works great with M80s (I have M60s), so it is interesting that a current model would have issues. The below information came from Audioholics web site (but was linked on their web site from another site), which is also where there bench test of continuous test tones over a 4 ohm load had issues, but "real world" as they put it tests came out just fine.
The SC-07 is THX Ultra II certified, and that spec states:
In 1999, THX launched THX Select, and renamed what had previously been called just THX to THX Ultra.
Whereas THX/THX Ultra was specified and designed for rooms "up to" 3000 ft3, THX Select took that requirement down to 2000 ft3. Both the requirements of the amplification and the output of the speakers were scaled back appropriately, placing THX in the hands of a whole new audience who could not have otherwise afforded it.
When it comes to amplification, continuous output tests are run on up to one, four, and five channels (simultaneously) of an Ultra product, but only one at a time on Select. With all products, the dynamic amplifier tests are done on up to all available channels. Ultra amplifiers must be stable on all channels to 3.2 ohms and swing an 18A peak, while Select products must be stable into 4 ohms (front channel) and 8 ohms (surrounds), and swing peaks of 12.5A and 6.2A respectively.
Source:
THX Ultra Specs I've had nothing but great luck with the Pioneer products I've owned. There is definitely some "brand loyalty" for me, however, I would look hard at another brand if I needed to drive 4 ohms just because I would rather play it safe. I am sure that there wouldn't be any real world issues, but still...
