The cross-talk issue can be solved by buffering each channel to a low impedance before the ADC - at the
standard 10kSPS rate 10k impedance is low enough, but at higher rates the driving impedance needs to
be proportionally less.
529kSPS is beyond the AVR Arduinos, not even SPI is fast enough. The MAX1139 is I2C and thus cannot
be fast enough for this rate - SPI or parallel are the choices for speed.