The above listed integrated amplifiers from NAD rated at 40/50WPC would be enough to power 2CH pair of B&W 603, KEF iQ9, Monitor RS6 or PSB T65? Or would I need an external amp from crown rated at 200WPC? Or should I move up a few notches from NAD integrated amplifier?

Secondly, Would I hear a noticeable difference in terms of sound quality going with a budget $400 7.1ch receiver as oppose to an integrated amp?

If suggesting integrated amps what other specific ones should I look at with the budget being from 100-700. Sound Quality is of course most important, no video upconversion needed.

Thank you.

I have a $300 Pioneer receiver and I think it's fine for casual listening, but I think the NAD would be a worthwhile upgrade. As far as whether you would notice it, it's not something that's going to make you say "ohmigosh, it sounds completely different", but you'll find the NAD just sounds a bit cleaner, the music may sound less strained, and maybe you'll notice more detail, and the music may get your toe tapping more. Usually the differences are pretty subtle even if you are concentrating.

The speakers you listed are moderate to high efficiency speakers so the 40W would be fine for small room, the largest 325 NAD would be suitable for a medium to large room. The cool thing about NAD is that it has soft clipping which means if you push the NAD too hard, it won't distort as easily and damage your speakers.

I don't think you can do much better than NAD in terms of pure sound quality in that price range. I'd also suggest Cambridge Audio line which are comparable.

I didn't reply before because I didn't know whether the speakers you named were big or small. I have the NAD C320 running a pair of 4 Ohm (drat! the forum sw can't do Greek) 30-80W bookshelf speakers in a reasonably large space: 5m × 6m with a 3.8m ceiling, with carpets and drapes. I have never needed to go past 4 on the volume even with the pub down the road.

Leave the "soft clipping" switch off. It's commonly known as the party switch, for good reason. The sound is audibly degraded even at low levels.