@Kingman -> and me, I have compared the Sunfire 400x5 in biamping mode through the JBL M552 xover to multiple high end amps and, at least in my setup, the Sunfire sounds as good. The only downside is that the elitist will accuse you of using home theater equipment in your systems ("you are putting chevy parts on a ferrari" and similar comments). Fortunately, all I care is how good the sound that the ribbons repreduce is, and to me it is good.
The Pass amps that courageous BJ is seeking to build look interesting and could be a home run, but my fear is building one (or worse 3!) and discovering they sound marginal or have a crazy untraceable hum that no one can tell where it is coming from etc. They could also be tough to sell if BJ is not happy with the result, so I have been harassing him to reconsider.
OBG