SPI vs Parallel interface for ADCs?
In your application it doesn't matter much, whether it's serial or parallel. Your bottleneck is going to be solenoid/physical movement of the fuel anyway (order of magnitude ms for solenoids, even less for fuel itself). That would put your attitude determination frequency in range of couple kHz max. 8 clock cycles at 600MHz is much less than that, I would worry about your control software implementation more. Just go with whatever is easier to implement, I suggest using SPI over DMA - just set it up to read all your ADC channel values sequentially, process them once all have arrived.