Not sure, I can check.

I'm beginning to wonder if it is not the preout voltage of my Denon, which I think is 1.2v and possibly it is clipping at the fuller power to the MPS-1. Below is a portion of the audioholics review I found, which appears to worry about some AVR preouts may have potential problems:

"I measured the voltage gain of the MPS-1 via balanced and unbalanced inputs and found the following:

Unbalanced: Av = 27dB
Balanced: AV = 26dB
Typical THX Product
Unbalanced Av = 29dB
Balanced: Av = 23dB (6dB lower than balanced)
It's a standard practice in most consumer and pro audio equipment that the gain structure of unbalanced to balanced is about 6dB less for the latter for power amps. The preamp therefore usually has a +6dB boost via the balanced outputs to compensate. I was a bit puzzled that the MPS-1 didn't follow this convention. However I didn't find it to be much of an issue, especially since the balanced outputs were about 3dB hotter than convention. It took about 1.65Vrms to drive the MPS-1 to full power. Had the MPS-1 followed standard convention of Av = 23dB some preamp sections of receivers such as the Yamaha RX-V2500 may not have been able to drive it to full power since that receivers' preamp outputs clip when output signals exceed 2Vrms. My personal criteria for amplifier gain structure is that it should be able to hit full power when driven with 2-3Vrms. The MPS-1 fell well within this criteria."

There is another guy on AVSforum that is having a similar problem with his Denon 2807 and his 4ohm Ref 1's.

I am not a electronics expert, but could this voltage thing be playing a part, or could it be my 4ohm 80's causing the problem?

M80s VP180 4xM22ow 4xM3ic EP600 2xEP350
AnthemAVM60 Outlaw7700 EmoA500 Epson5040UB FluanceRT85