Granted my sample size is small at only one, but I heard people waxing poetic about no preamp. So I ran my Audiolab 8300CDQ directly to my Aragon Palladium 2 monoblocks. It seemed good. Until I hooked a preamp back up. Holy moley, a ton of detail, separation and soundstage came back. The 8300 has a "class A" preamp section in it with a digital volume control. It could not compete with a preamp.
It was enough of a difference, that I don't plan on not using a preamp again.