I think we need to take a step back with the issue of EQ settings.
The aim of any sound reproduction setup, is to recreate a sound in your room, as close as possible to the original live version.
It matters not, whether we are talking about your favourite Hi-Fi system,a Clavinova or indeed any keyboard/amp combination, the aim is the same.
Generally speaking, the more expensive the the setup, the less user adjustment is required to achieve that aim.
Manufacturers such as Yamaha, go to great lengths to ensure that the frequency response of their equipment is flat/level throughout the entire audio frequency range, whether it be the extreme low bass sounds, or up to the high treble notes and i believe, with the CVP800 series pianos, this aim is largely met.
Any adjustment away from the makers standard setup is really only necessary to suit music room acoustics and personal choice.
Room acoustics are influenced, in the case of high frequencies, by carpets and soft furnishings, and low frequencies, by room size and shape, oblong is better than square, with the instrument located against the short wall.
However, very few of us have the luxury of choosing room shape or even position within the room, hence the need for some form of equalisation.
In my case with my CVP805, I run with:- 1. Mixer/Master page, Comp = Natural, EQ = Flat, (the default setting) when on speakers. 2. Comp Output = 77, EQ = Flat, when using Sennheiser headphones. 3.Comp = Natural, EQ = Bright, when using Yamaha headphones, but as I said at the start, its all a matter of personal choice. It should not really be necessary to adjust intermediate frequencies.
Moving on, if you find that certain voices in a particular style are overpowering, eg strings are louder than piano, then adjustment should be made using the Balance page and/or Mixer page, Panel and/or Style settings.
I'm about 5 weeks into ownership of my 805 and i'm liking better each day