A21 vs McCormack?

I will also recommend McCormack and SMcAudio, as the work they have done for me is beyond reproach.
I have no knowledge of Parasound, but have known the brand to be of very good quality.
The question is what are the other components of your system?
I hate the trite term 'synergy', but it really does come into play.
Bob

My DNA 0.5 is the only piece of gear I've regretted selling.Nothing against parasound, but the McCormack have a following for a reason.

Thanks for your responses — Bob, the rest of my system is:
Usher Mini Dancer 2’s
DNA-1 
Parasound 2100 preamp
Benchmark 1 DAC
Bluenote Vault
Cambridge CXU
Technics SL-D2 (rarely used)

I was planning to upgrade the DNA-1, but the recent cost drop of A-21’s, due to the release of the A-21+, made me wonder if that would be a more cost-effective choice for an amp of similar quality. I’m surprised no one has spoken up for the A-21’s, as they were John Curl design and I had heard they were very, very good. I’ve been very happy with my McCormack, and have heard SMC does a great job with the upgrade, but before spending $2K I wanted to be sure I wasn’t overlooking a great, lower cost alternative. 

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.