Analog input buffer for an A/D Converter - what op-amp to use?
Not really. The opamps are configured as pretty basic unity gain buffers with an output low pass filter feeding into the ADC stage. This means they don't need much gain-bandwidth capability, much output current capacity, and even the input impedance requirements are not that important. As the system is working with audio, the input offset voltage isn't that important either.

The main requirement you need to watch will be the input and output voltage range with respect to what the ADC expects and the power supply you have available. Any low voltage rail-to-rail opamp should be more than adequate in this regard.

Given that this is an audio system, I'd say the most important characteristic will be the noise and distortion performance. Opamps operating as buffers have very low THD anyway, but some people believe you can hear even tiny amounts. Noise, however, will be something that is quite apparent if you choose a bad opamp, and I would probably focus on minimizing this as a priority.