Going from the Adcom GFA 555 ii to the Bryston 4b SST or SST2?

I had the Adcom and the Bryston 7Bst, and 7Bsst2 (super Stewart Taylor after the inventor). I have never owned a 4B in any iteration but I can say that the 7Bsst was warmer and faster than the Adcom. I drive Maggie 3.7s- the first gen and the X. For my liking the Bryston solid state sound is better than my Pass 600s were and better than the Audio Research VT130 was (mostly because tubes can have flabby bass with Electronica).   If you have low efficiency speakers and like volume Bryston has the guts to drive them hard for long listening periods. 

In my opinion, the Bryston will make you never look back at the Adcom. I have had Adcom amps for 40 years, converting most of the generations of the amp line. When I switched it was night and day. Definitely not shrill in the upper end, or sterile. The low end absolutely came alive with so much more depth and emphasis. 
 

i am currently running Bryston 7BSST Monoblocks from an Adcom preamp (which will be upgraded soon) into B&W Matrix 801s3. 

Going by memory. 32 years ago in a controlled environment at my Dealers showroom in Hamilton, Ontario. On a pair of Mirage M7si’s that I was going to purchase. He played tracks from On Every Street on two separate Preamp/Amp combo’s

He knew my budget would allow for Adcom not Bryston and I was curious about ROI between the brands. 
 

I could not hear a difference ! Being Canadian (but living in Phoenix for the last 10 years). I’ve basically written off Canadian Audio Electronics brands since then (plus none of them would hire a freshly minted Tech from my local CC).

I enjoyed that Adcom GFP-345 w/phono preamp option and GFA-545II (later traded up to a 555II 7 years later.

Selling the preamp during the home theater craze of the early 2000’s was a mistake but the 555 (used) got another 15 years of use before it went “up in smoke”. 

I had the 2B SST on demo in my system and although good and very neutral I found the treble a bit tipped up and overall a bit thin sounding relative to my McCormack 0.5 Rev A amp (now upgraded with their later G22 upgrades), so I’d definitely focus on the SST2 as that’s supposedly a bit more refined up top.  

That said, I brought my amp to my friend’s house who has a 3B SST2 and both of us much preferred mine as it had better tonality, dynamics, and an expanded soundstage.  In short, my amp sounded more natural, robust, and refined despite being the lower-powered amp on paper.  I bring this up because this DNA 1 with the same upgrades as my amp just became available for $2400, which is basically the price for the G22 upgrades so you’re basically getting the amp for free, and it’s about the same price as a used 4B SST2.  Without hesitation I would jump on this amp as SMcAudio-upgraded amps are considered near SOTA, and you’re basically getting a near new amp as the upgrade basically just keeps the case and all the internals are new and likely done within the past five years. Bottom line — I’m confident this would blow away your Adcom on every level.   Just my $0.02 FWIW, and best of luck.

https://www.usaudiomart.com/details/650246512-smc-audio-mccormack-dna-1-gt-22-ultra-amp-shipping-included/

You are likely looking at 2nd hand. Assuming you are running single ended(555ii), purchase an ADA PF201. A real sleeper of an amp....and I know.