As an ex designer of opamps understanding the trade off benefits is not much of a problem, and I am quite circumspect when I make the exchanges.
One issue that I have with the 5534 family is that, and please correct me if I'm wrong, no distortion measurements are provided in the data sheet, although they were partially assessed by Sam Groner in 2009.
Replacing the 5532s with the 1612s did provide measurable performance improvements in distortion- 2-3 orders of magnitude if I remember correctly- and in the circuits that I looked at some other performance improvements- nothing earth shattering, a bit lower noise in an input stage, less 20kHz roll off in high gain stages due to GBW limitations- it also provided me with a bit of amusement.
I was checking the 5534/2 specs and glanced at the On Semi datasheet for the parts and immediately noticed something strange in the equivalent "schematic" they provided for the 54.
https://www.onsemi.com/pub/Collateral/NE5534-D.PDF
The input stage current mirror biasing cannot work.
The 5532 schematic is correct.
https://www.onsemi.com/pub/Collateral/NE5532-D.PDF.
I believe that the discrete opamp that was alluded to earlier is this one,
https://sparkoslabs.com/wp-content/uploads/2018/03/SS3601_SS3602.pdf
The open loop phase characteristic is very interesting to say the least- supporting Maty's observations earlier- and there are comments made on the ability of IC opamps to include various capabilities which are not correct. It's also interesting that the data sheet doesn't include any square wave response plots that are not in a limiting case (slewing, clipping, current limited).
In any case, at least they make some attempt to be professional. I've tried, without success, to find any detailed information on the Bursons besides this "datasheet"
https://drive.google.com/file/d/0Bxn23njCr8VCR19ELS1YOTMxV00/view
Many people claim performance improvements such as "lower noise", "more extended bass", etc. which one would think would be readily derived from specs. However, as far as I know no one has ever actually measured these improvements and there seem to be no ABX tests to be found to justify the statements of subjective improvement.
Sam Groner was less than complimentary about an earlier Burson amp
http://www.nanovolt.ch/resources/ic_opamps/pdf/opamp_distortion.pdf
Is anyone aware of any technical analysis/teardown of the recent Burson offerings?