I have finalized the testing of the prototype and I am happy to say that I managed to get the noise to -70dbu (20-24KHz) with a 600 Ohm load... this is less 0.25mVRms of input referred noise for the bandwidth from 10Hz-24KHz. This is 1.58uV/Hz^0.5 of input referred noise. Maximum noise is at -60dBu (with 10dB gain)
That means that while the noise will be still audible (-90dBFs for a 0dBFs=>20dBu interface, so barely 6dB above the 16 bit dynamic range) but should be low enough to be usable as the last element of a chain.
For me the golden standard is -76dBu, that is achievable by reducing headroom. Right now it is calibrated to a +28dBm max input, but it should be possible to reduce the noise level even more