You mean as an effects device into a tube amp? Yes, but it's really overkill for that purpose. It's meant to replace your tube amp. They emulate (my technical wording may be off) speakers and cabinets. They're important because they dramatically affect the sound. Note: if you're using the Axe as an effects device into a tube amp or (as many people do) into a separate power amp and guitar cabinet (as opposed to for recording or playing through a FRFR speaker) then you will have cab emulation off and they will be irrelevant. Tons and tons and tons. Start with the description of the product on the Fractal website. Maybe look at the Axe-fx2 FAQs.