Hi MadrasGiaguari.
Thanks for your query, first let me say i have no real knowledge of the overall sound levels of the CVP809, so cannot truly compare the two pianos.
Obviously I have heard both pianos in the demonstration setting of numerous videos and the odd dealer, but cannot tell any significant difference in overall sound quality between the two.
Many years ago in my youth, I had a part time job at a top class HI-Fi shop selling equipment, so do know a bit about sound quality.
i can say that the 805 with its simplified amp/speaker system and total of 130 watts of power, has more than enough power to 'blow your head off' in the average domestic setting, I guess the CVP809 wiil be somewhat louder, but hey who's counting?
My previous piano was the CVP605 and even that, with its 90 watt total power, was, in my view sufficient. I'm not a lover of heavy metal, 'thump thump' type bass, as i prefer a balanced sound output throughout the frequency range.
Having said all that, for me the biggest difference with my upgrade, is the sheer quality on the new voices, they are are more realistic, crisp, lifelike, don't know how best to describe it.
Its like being in the band/orchestra or whatever, you just don't need the sound to be over loud to get the best enjoyment.
You will see in previous posts, that in deference to my neighbours, much of my playing is on headphones, but I do occasionally get the chance to 'let fly' and rattle the windows!!
May I suggest that you visit your local dealer, for a demo on both models, as in the end it all comes down to personal choice. Certainly I have no regrets in choosing the lower model, I just couldn't justify the significant extra expense of the CVP809 for what are for me, only marginal improvements
I hope that my comments are helpful, but if you have any further queries, then don't hesitate to ask.
Stay safe and best regards Ken.