When I owned Sonus Faber Concertinos I also owned both the Electrocompaniet ECI-3 and Simaudio Moon I-5 integrateds.
I must admit that during this period I had room acoustic and cabling issues, so my experience with these units isn't what I would have hoped for.
When comparing both with the Concertinos, I thought the ECI-3 was smoother and not quite as tipped up in the treble as the I-5, both sounded much stronger than 70wpc. Both amps were quite spacious and soundstaged well, but I would have to give a slight edge to the I-5 in this area because of the extra sonic cues that an extended treble can sometimes yield. The overall balance of the ECI-3 was more in the direction of tube sound than the I-5, but I still wouldn't characterize the sound of the Electrocompaniet as being tubey. The ECI-3 has a clean, elegant design and the remote works very well with the unit.
I sold both units, and the only reason I didn't keep the ECI-3 was because of what I suspect as being an impedance matching issue with my NHT SW3P subwoofer. It's possible the output impedance of the ECI-3 was too high to properly drive the NHT sub amp. Bass was very strong in the upper regions, but lacked any extension on the bottom end. I had to turn the gain of the NHT way up to get any lower octaves and that completely unbalanced the sound. I don't know what the specs or the input impedance of the amp used by your ASW600 is, but I would compare the Classé and ECI-3 to make sure the B&W's input impedance is at least 10-100 times that of the integrateds pre-out output impedance. Hopefully this won't be an issue.
Overall, I thought the tonal balance of the ECI-3 matched to the Sonus Fabers was organic, yet dynamic. I wish I didn't have so many deficits in other areas of my system because I think I could have really lived with this combo. The Concertinos are the most beautiful monitors I've owned. Excellent build quality and a very classic appearance.