I know of three people using the Panny receivers with great success. One person triamps his Apogee speakers, another replaced his modified Marsh amp with a 700 driving his $10,000 Merlin speakers and another runs $27,000 speakers with modified $13,000 Esoteric transport with stock 700......he says 700 noticeably better than 57.
Don't think there are any other fully digital receivers that I would choose over the Pannies.
Basically, the Panny changes the PCM digital input directly to PWM.....whereas most switching amps change analog into PWM. Keeping it pure digital is way cool.
You will have to modify the Behringer with digital outs to get the full advantage of the Pannies.....you really don't want to use the analog path in the Behringer and the analog ins on the Pannies.....go straight digital. You can get the digital out board from switch-box.com and install yourself or have one of the modders do it for you. You would want to change the digital input jack to coax too. As long as you have a source that has digital input you would be good to go......of course, you could run analog into the behringer and digital out....you could use that with a source that is not as critical and keep the digital coax for your serious source. A couple of 700s or even 57s run this way would be super and relatively inexpensive.