I have done several listening tests comparing the THAT 1510 with the INA 217 opamp, and have to conclude that the differences are very low, and if I have to choose I would prefer the THAT 1510.
I did not hear anything of a high frequency hype as was stated earlier in this thread; IMHO there is a lower distortion in the higher midrange from the THAT 1510, which opens up that part a bit, which make the top end seem to be sharper, but this certainly does not cause a hype in the higher tonal band.
On very dynamic vocal material it seems to be the THAT 1510 handles that better, the INA 217 leaves you with some kind of pressure on the ears.
The SSM 2019 I have not heard, on paper this one has the highest distortion compared to the others. Maybe higher distortion in the low end makes it sound more warm.
Please any opinions are welcome.
Erik Sikkema