I assume that you've tried all the different amps, preamps, and cables using your AMR dac as the source. If you are getting the exact same problem with all of that equipment, the dac may be the problem. I know the problem doesn’t happen when you run it straight into the amp but that doesn’t rule it out. Aside from the volume control on the dac, it may have global gain settings as well. The gain from your dac plus the gain from your preamp may be too much. I can have the same problem with my Wadia. When I use it with my Wilson speakers, I have to open it up and lower the global gain using a row of dip switches Wadia gives you just for this reason.
I'm not saying this is definitely the case, but its definitely worth looking at. If it turns out that you don't have any global gain settings, try going from the fixed out to the variable out on your dac and lower the volume manually.
I'm not saying this is definitely the case, but its definitely worth looking at. If it turns out that you don't have any global gain settings, try going from the fixed out to the variable out on your dac and lower the volume manually.