my receiver is the SR5005, last year's model, and i use it as a pre-pro
(except for the surround back channels, which are driven by the Marantz).
so, when i listen to something, it's mostly through the preamp, and when the sound source is of high quality, it's totally transparent; which means that not only the speakers are superb but also the preamp.
they just disappear...

no noise, no discernable distortion, flat Fr. Resp., great dynamics...

See: http://www.blu-ray.com/community/gallery.php?member=Gelli
or: Axiom Gallery