A21 vs McCormack?

I'm a huge fan of McCormack upgraded amps and have had multiple amps upgraded by him to platinum level.  In fact, I just talked to him a couple days ago and will be sending my DNA125 to him soon for a new upgrade he just discovered which he says is his biggest improvement yet.

However, based on your system, I'm NOT going to recommend spending money on upgrading your DNA1 (or buying the parasound). 

I also own your Benchmark DAC1 (although it's long been retired and just used for gaming PC/headphones now).  I would swap out that DAC before messing with amps.  Trust my experience.  You won't fully appreciate the upgrades of the McCormack amps until your source is up to par.

I'm trying to help you with priorities if you're on a limited budget. 

Your existing DNA1 is plenty good enough for your associate gear right now.  It's true that your existing amp won't be to the level of McCormack upgrades which bring things to true reference levels at an affordable price, but you have far more deficient gear at this point.  If I had your system, my upgrade priorities would be...

1.  Subwoofer (ideally a Vandersteen sub) to give full range performance unless your room is really small and the Usher's GENUINELY deliver full-range performance which I highly doubt.
2.  Room treatments/Dirac - Take measurement and treat your room accordingly
3.  New DAC - the DAC 1 is long in the tooth and it is a little harsh.  Benchmark didn't solve the problem with intersample overs until the DAC2, but even that DAC isn't my favorite.  Bottom line...It's time to get a true state of the art DAC. DACs depreciate much faster than amplifiers because advancements are much more prevalent and audible with new technology.  The DAC1 is no longer SOTA.

Once you have a full-range speaker system with a room treated to deliver near optimal response, then you should get the new DAC.  After that it will be the optimal time to get the DNA1 upgraded, IMO.

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.

McCormack for sure. 

Everyone -- thanks for your responses; it's a big help in deciding how to move forward.
@labtec: thanks for your detailed message and suggestions.  I'm having some trouble with my DNA-1 now, so I don't want to put this off any more; the issue was whether to send it to SMc, or go with another amp; given all the current options with Class D and other lower cost solutions, I thought I should explore it a little before going with the rebuild.  From all the responses, I think the rebuild is the right way to go.  However, I appreciate your advice on setting my other priorities; I have been fairly happy with the Benchmark 1, but I realize it's not SOTA.  How much do you think I should budget for an SOTA DAC that would complement the rest of my system, and would you recommend new or used?  As for the subwoofer suggestion, that is on my radar, although I'm planning to go for a swarm after I get the amp and DAC budgeted.  Thanks again!

@cheeg, 
For the money, I would get an Ayre Codex for a DAC.
Used, they are just a bit above $1K these days.
Or, a Schiit Gungnir or Yggy.
Both companies offer upgrades, and have very detailed sound, in my humble opinion.
Also, if you can ever score a broken DNA-1, SMcAudio can convert them to monoblocks. All they need is the case, everything gets scraped and overhauled. They did a pair for me a couple of years ago.
Just be sure to tell Pat or Steve what equipment you are using, they can tailor the amp to whatever you own.

As far as Class D goes, I would give it a couple more years to mature.
Yes, they can sound great, but I think staying with A or AB amps would be the safest course, for now. Again, just my opinion.

Bob