everything sounded great until the upgrade

I would suggest seeking new cables with larger diameter conductors. Synergy between the components in the modest system was probably achieved. Changing the component requires adjustments.

With Interconnect and speaker cables and any conductors in the components themselves (traces on the PCB, internal wiring), at least in the audio spectrum,  a larger conductor will yield more emphasis on the low end of the spectrum and a smaller conductor will yield more emphasis on the  higher end of the spectrum. The sum of the signal path, the matching of all the component should amount to an audio balance that fits your taste.

Maybe the internal wiring of your two amps are of different size and yield different tonal response (high end or low end emphasis). If you can manage to identify the diameter of the isolated conductor in your IC and /or speaker cables, You could try to other IC and/or speaker cables with larger conductors to get back to the tonal response you had with your previous amp.

For instance Duelund offers relatively inexpensive hock up wires of different gauges and compositions, It would be interesting to try them if you can put together the IC or have some one do it for you.   From there you may find the gauge or wire that will make your system synergistic again.

@itsjustme 

Why did you buy something without hearing it first? 

Because it's used, can't hear it anywhere

@mahgister 

design change is less impactful on listening test than acoustic and psycho-acoustic change in the speakers/room relation

Right. But when my room is a given, not many options in placement, my main variables are components and cables - as I stick to the speakers

1 week update:

the sound from the MF A3.2 is definitely different. I noticed that different types of music sounds good with it, and so I changed what I listen to, all the instruments are brighter, more forward, vocals less harsh, less punchy.

haven’t gotten a DAC yet, but I certainly appreciate the experience and the quality, It does bring out recording flaws, which - given my selection of 60s-80s mostly - is a pain, because recording back then was less than perfect (but also, some were tweaked until it sounded best)

Playing LPs is much more fun now. (need a new cartridge, then a new turntable, then I will find my suitcase on the driveway)

thank you all! As much as I often find some of you arrogant and egoistic pricks, most of you are awesome: generous, helpful and knowledgeable! :)

@felixa 

I need you to explain this to me via zoom!

No need to ever turn the amp off unless you are plugging or unplugging cables. Just make sure you turn down the volume when you turn  your source on or off. Eliminates warm up time and sounds even better after beiding played for a little while.