No way you can compare the 500 series to the 800/900. I played the 800 for 4 years, 500 x a year. I bought the 500 for a backup and it was like a toy in comparison, thus the reason it doesn't sell well.
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Yamaha 920 / Yamaha DGX-670 / Maui 5 Go (2) / Senn e935 / Sony C80 / Tascam DP24sd / ATEM Mini Pro switcher (studio)