I did a similar test. I ran my A800 with a set of Sansui SP20,000 and Kenwood MV-7, both large horn loaded sensitive speakers. Running optical from PC to the Emotiva PT100 Preamp/DAC, the PC and A800 max gain then controling volume via the PT100 I put on HD Tracks hi-res sampler. To me excellent dynamic range and detail, dead quiet during breaks and pauses in the music.
For comparison I took an old cheap Sony STR-DE185 stereo receiver and put in place of the A800, played same songs and quickly the horns exposed a bit of distortion and hissing. I know the A800 isn't the best amp out there but it definitely is a great one for $300. An excellent amp for listeners on a budget or just getting started.
There are some critics that will point out the possible distortion created by the A800 amplifier. However, there are others who will also simply point out that the distortion created by a speaker would be much greater than that of the amplifier itself.
With that being said, my A800 arrived yesterday. I installed in in place of my $45 "special" A500 amplifier, also by Behringer. To me, both sound and perform quite well. The A500 has heatsinks on the left and right sides of the amp, where the A800, being class "D" doesn't have them. The A800 is a few pounds lighter and about 1" shorter in depth than the A500. My ears could discern no real sonic differences between the two amps and in my condominium, I'm certainly not utilizing all of the power that each one can provide. Though, I do have 2 10" 500 watt subwoofers for bass duty in my music below 70 Hz. In fact, for my needs, both amps performed quite well compared to my 42 Lb. amp and the 57 Lb. Emotiva SA-250, which I sold a few weeks back. While the release of the Purifi amps and higher-powered Hypex amps is interesting, I don't find myself making any amp changes anytime soon. Well, that is unless the Behringer NX6000D, available locally as a used amp, doesn't tempt me if the price is right. :O