As I've said elsewhere, if you set your guitar-input level correctly on the KPA and record and play that back to it at unity gain, you'll never have to think about levels. The signal-to-noise ratio is irrelevant with any decent modern interface, as I also said. I'm speaking specifically about DI and reamping, 'cause that involves more than just the route into the computer and is therefore the "ultimate" test of the efficacy of the analogue method.
Doesn't this depend on the profile that you choose? For instance, I would always set my gain on my inteface higher or lower on high or low level gain profiles. The gain would even change on various profiles from the same author (Bert Meulendijk), which are fairly well balanced volume wise.
Does S/PDIF completely eliminate this problem?