My thoughts . . .
I suspect, its not only the camera phone video, but
that we're merely hearing the BK-5 thru its built in speakers.
I will reserve my judgement about the sound until I hear a demo
digitally recorded directly from the keyboards audio outputs,
as this is the same negative press the TOTL Korg PA3X
got when only heard thru its optional & rather pricy auxlllary speakers,
Considering that fact, "relatively speaking" of course,
the BK-5's built in ones don't really sound so terrible.

Scott