1. NO mic input
2. Grey scale screen (not bad)
3. Less polyphony, styles and sounds

I really liked the 500, but for the money, the 800 is just way more for little money.
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Yamaha 920 / Yamaha DGX-670 / Maui 5 Go (2) / Senn e935 / Sony C80 / Tascam DP24sd / ATEM Mini Pro switcher (studio)