I know the "Pilots Guide" is lacking in some technical aspects, such as what patch cables to use, (i.e. TS, TRS, RCS, etc) The 1/4" Main Outs are only for plugging into a destination such as a mixing console, PA or powered monitors. The only way I know of you connect to an amp like a Marshall, Fender, etc. is to go from "Amp Out" to the "input of a guitar amp", in which case Bluetooth audio will not be present at the "Amp Out" and thus not present on the Amp either. It does say you can use "Mains Outs & Amp Out together" in which case the Bluetooth audio would be present at the "Main Outs" (i.e. patched to 2 powered monitors, a PA or mixing console. What I'm seeing, since I have it only patched up to my home theater stereo system is that I have to bump the volume up on my home theater stereo amp to get decent volume and this is with the volume on the Amplifii TT up at about 3/4. I haven't played a lot with the volume on the remote app for each amp yet, that might bump the volume up some. I've only had it a day. I'm used to playing through a Marshall half stack or a Fender.