Well, my wife and I just finished the Bolero Test as described by Arthur Salvatore at high-endaudio.com. Basically, we played Ravel's Bolero directly from the Rotel CD player to the Amp and bypassed the integrated amp completely. Our findings playing Bolero directly from CD player to amp:
1. The volume was much louder than our normal listening level.
2. Better separation of instruments.
3. No seeming lost of bass.
4. Horns seemed to be a little sharper. Brighter?
5. Sound seemed more natural.
We went back and forth a few times. The first time through, my wife didn't know what I was doing and made similar observations to the ones above. I preferred the sound without the integrated amp, although the horns were a bit sharp.
I'd be interested in doing this as a blind test, but we both thought the differences were very obvious. Will placing a passive amp in between the CD player and the amp likely result in similar results?
By the way, as recommended by Arthur Salvatore, we only played Bolero because it starts out soft. I was afraid to do it with another piece of music because the volume direct from CD player to amp was so loud.