Hiya

I have both and to my ear the N810 produces a bit better sound.
I'm not a technical expert or a musician but I will try to describe my experiences

I've conducted a few tests with different pieces of music, pop, classical, jazz

The speaker sound quality:
1. The sound of the 810 seems a little richer, wider frequency range, the bass is definitely deeper, you can even feel this trembling if you hold the tablet in your hand
2. Stereo effect on the N810 seems much wider, it's because of the speakers location, it is projected sideways.
3. Maximum volume level on the N800 is a bit higher, probably because the sound is projected directly towards the listener.

The headphones sound quality:
I can't hear any difference in quality/volume.

The biggest difference is when I connect the tablets to my car radio using a standard jack-jack cable. The N800 produces very hissy sound, which makes it practically impossible to listen to any music while the N810 is almost crystal clear.

Hope it helps