Meanwhile, I asked Sudclavier about the recording quality of the video, and their answer is:
"Bonjour et merci de votre message. Le son de cette vidéo est du MP3, cependant le son que vous pouvez entendre dans la vidéo est tout à fait identique aux sons proposés par l'instrument. Cordialement"
They say the video has normal MP3 audio quality and what you hear is practically identical to what you would hear directly from the E-A7. So, I strongly suppose that some sounds like brass and sax sections are implemented in a compressed way compared to the BK-9, you shouldn't expect the same sound quality throughout all the sound range. Pianos, drums and other sounds seem perfectly ok to me, but with others Roland obviously saw the necessity for compression in view of the thousands of sounds implemented. More quantity than quality, I fear.
Anyway, as long as there are not even official audio demos on the global Roland website or by Roland Corporation on Soundcloud, my doubts about the sound quality will be further nourished.