i find i can only put on my critical listening hat for short stretches. It gets unreliable otherwise. Once i come to some conclusion abt what i'm hearing i just switch the critical listening off and go enjoy the music.You subjective experience would be good for me if you can't provide a thermometer measurement. (Maybe there are things that doesn't need a measuring tool, but don't expect me to trust your "feelings" about SNR of the device )
Found that the LM4562 which you can order the A07 non-Pro with and which i did, is worth getting. The OPA1656, the ones i got which i think are genuine but i didn't buy them from a certified TI distributor, isn't all that different from it. Used in this A07 Pro amp, i hear a wider dynamic range with the OPA1656 and more emphasized treble with a little better detail, along with a more defined low bass. They're small if distinct differences that show up best at high sound volumes, not big differences.
Right now, when i'm just playing music to enjoy it, i can't swear to you that i hear any differences between them.
Neither of these op-amps will give you a tube amplifier sound. They're solid state neutral, don't introduce any harmonics as tubes will.
The AD827 seems to be a mixed bag. i've not been using them for a bit and don't have any conclusions abt them when plugged into this now broken in A07 Pro, because i haven't done it.
For a lovely, smooth and silky solid state sound from a cheap device, check out the Fosi Audio BT30D Pro. It's also a TPA3255 amp. It's a 2.1 amp with separate volume and frequency controls for a passive subwoofer. It's unusual in that it uses a second TPA3255 just to drive the sub. Didn't unscrew the heatsink when i had it so can't confirm that.