Noise measurement with soundcard and REW

[noxet]

Alright guys, I figured it out after all, I was of course the idiot here..
I did calibrate using REW, which sweeps and measures the response. This calibration I saved as a calibration file and have used it on every measurement since.
As magic pointed out, of course REW needs to know what ADC value corresponds with the actual voltage. I did this calibration too in the RTA tool. This, however, did not get saved in a file, but was just cached in the software itself, and for some reason, was not applied when I tried to measure the op amps. 

I finally re-calibrated it, feeding a known sine wave from my function generator, and entering the rms value in REW. Now everything looks good, and after redoing all the measurements with LM358, TL072, and an OP07, it all matches with the datasheets! 

I want to thank all of you for your input here. It has been really helpful and I have adjusted my setup accordingly with much lower gain, resistance values etc.