It really depends what you partner them with. If they're paired with say a Cyrus 6 or 8 amp, they're likely to sound a little bright and muddled at higher volumes purely because the amplifier isn't particularly powerful. Similarly so if they're parnered with budget amplification, which would be the case with many qality speakers anyway. I've heard one or two of the entrey level ones to be a little edgy, but they are exactly that - entry level.
We've used ProAc with Naim, ATC, Arcam, Quad, Rega, Audiolab, Primare, Roksan, and Cyrus (new 6 and 8 amps and pre/powers) and never really found them bright. Primare and Audiolab with them wasn't my cup of tea, but the other work fine. I've heard them sound bright with certain CD's, but that's because of the way the albums had been mastered to CD.
Generally, ProAc tends to have a fairly sweet sound, erring slightly on the warmer side of things, and tend to be very listenable with many styles of music.
The D2 is pretty much a standmount version of the D15 floorstander, which was a fantastic speaker.