DIY amplifiers in this class get expensive quickly, because onesy-twosy parts costs are ridiculous (those big smoothing caps might cost you $50 each), and if you want professional results, like the DIY speaker guys get, then you'll want multi-layer, two-sided PCBs and a custom chassis just like Moon. It wouldn't surprise me at all if building just one - and only one - of these Moon amps DIY cost over $50K, and that's assuming you could design it yourself. (I suspect chassis and board costs would swamp everything else.) Hmmm... DIY amp or kitchen remodel... I think I'd rather go appliance shopping.
I'm not suggesting building an exact clone of the 870A.
I'm suggesting building DIY that could match it in PERFORMANCE. I'm not worried about aesthetics, so any $ that would go to that can go out the window. Also, when you go the DIY route, you often re-purpose parts from old electronics and old projects, so that saves $ too (granted, I did say "cost no object" in my first post).
There are many amplifier schematics/plans available, so take that $ out of the equation too.
What I'm saying is that $22K is silly-expensive. I bet a DIY could achieve "as good" performance for 10-20% of the cost of this Moon.
Edit:
On a side note, looking at the Moon site, I see a few interesting items:
*This is a "no overall feedback" topology
*I'm curious as to why they used BJTs on the outputs instead of MOSFETs?
*Output impedance <0.01ohm
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wowza!
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*S/N is "only" 106dB???
*Teflon-insulated wiring--NICE! What a luxury.