Polarity test with DMM

The BP1200.1 can normally handle a 1-ohm load, although the distortion numbers go through the roof at that low loading.  Some BP-series amps will not remain stable at 1-ohm, so it could be that.

To both posters above: you cannot, repeat CANNOT set yuor amplifier gain by guessing what the HU output might be and then simply adjusting the pot to, oh, about that point.  You must set it up so that the amplifier input sensitivity matches the HU output.  This requires meters and experience to do it properly, but it can be done by ear using a method described in this forum multiple times.  A quick search found this thread, as an example.  There are others as well.

In the case of a high-voltage HU like the Eclipse, you can use it with an old design low-voltage amp as long as you never turn the HU volume up too high.  You can discover the point of max output by setting the amp gain to minimum and slowly turning up the HU while playing a test tone until you hear the tone change (amplifier begins to clip.)  This would indicate your new MAX HU VOLUME.  Or get a new amp designed for high voltage input.