Can I send audio into the analog input and get it out of the digital output on the G-Major / G-Major 2? I want to use it as an external A/D converter for another unit.
Both the analog and digital outputs of the G-Major are active all the same, so the G-Major constantly sends out S/PDIF, regardless of the input settings. This means, it will work just fine as an outboard A/D converter.
Be sure though, to set your audio interface / other device to slave to the clock coming from the G-Major! This can be called several things depending on the audio interface, like 'External sync', 'Sample rate > Ext' and so on.
Please refer to the product documentation of your audio interface / other device or ask the manufacturer when in doubt.