Here's a page with photos of some actual recording sheets (for "Anyhow" among others) where you can see how the Sans Amp was set. The Sans Amp GT2 pedal was made to be used as a line-in effect between a guitar and a mixer (hence the name; "Sans Amp" which means "Without amp").
I play through my 1968 Fender Showman which has a very clean sound at all volumes. I never did care much for the sound of line-in recordings of guitar though and that's why I only use it as a "normal" pedal between my guitars and my amp.
I see no problem in that, even if you're trying to get a vintage'ish sound.
Quite on the contrary actually: If it hadn't been for cheap hi-res sound cards, I could never have afforded to experiment and record as much as I have.
One for beginners called "How to play rockabilly guitar, and get good, fast!