Preamp Noise with High-Efficiency Speakers

I have Avantgarde Duo Classic Speakers, I hear a very audible buzzing noise whenever I insert an analog preamp. If I run my DAC (AMR DP-777) directly into power amp, the noise disappears. I have tried 4 different preamps (tube and SS), 3 different amps, a bunch of RCA and XLR interconnects, the problem persists. I have tried dedicated power line and two power conditioners (with Multi-wave options) and various high-quality power cords, so far nothing works, and I am forced to run DAC-direct into power amp. The buzz is not very loud but certainly audible enough to be annoying. There's no noise running the same equipment and power source into regular speakers, I am pretty sure it's just the Avantgarde (104dB sensitivity). Please share your solution if you have had similar situations. Thanks!
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.
Good comments by the others. One additional thought:

By any chance have the preamps you have tried been located close to the DAC or the source, perhaps just above or below it or them in a rack? While is the power amp located several feet or more away from those components?

If so, it could be that the DAC and/or source are radiating digital noise into the preamp. If that seems like a possibility, try locating the preamp a few feet away from the other components.

-- Al
It is encouraged to have low-gain low-power amplifier for high efficiency horns and same applies to the preamp that should be minimalistic. I belive hat Wyred4Soun preamp may surprise you, but I'm not sure what amplifier(s) you're currently using
This could be caused by a ground loop. A ground loop can exist if your equipment is built without a proper grounding scheme.

If you float the ground pin of the amplifier power cord from the wall (using a hardware store ground cheater) and the buzz is solved then it is the amp. If this works best on the preamp than the preamp could be at fault. In either case it is not recommended to operate the system without the equipment being properly grounded- there is the risk of shock or fire hazard if a component develops a fault.

If you are able to sort out which component is the culprit, you will have to come up with a solution. The best solution is to have a proper grounding scheme installed in the defective equipment. If the manufacturer gives you pushback on this have them give me a call (seriously- setting things up right is not that hard).

Otherwise an isolation transformer for the problematic unit could sort things out.
Thank you all for the very insightful suggestions. I'll do some experiment early next month. I will try removing the ground pin (on power cord) one by one, and then try a passive preamp to see if it's a gain issue. I've had a Benchmark DAC-1, even at 0DB setting (10 volt output on XLR!) it is dead quiet with the same pre/amp. Will report later.