The A-21 is a great, powerful amp, maybe one of the best under $3k amps around, made in China. The McCormack DNA-1's are legendary bulletproof amps, deluxe versions comparable power, made in the USA. When you talk about "newly rebuilt" Gold McCormacks by Steve at SMc, about 3/4 of the guts are replaced with new upgraded parts. I've owned both amps at the same time and the Mc won for me. I've had other upgrades and mono conversions done by Steve also and that's one of the benefits of his products, service and upgradeability. I guess the point of this post is leaning towards the McCormack.
A21 vs McCormack?
If you had a choice between a new Parasound A21 and a newly rebuilt (Gold) McCormack DNA-1, which would you choose and why?