There is nothing wrong with the NAD C352. But these comparisons can be somewhat skewed and it is important not to put all your faith in a review where a product gets 4 out 5 or 9 out of 10 versus something they give 5/5 or 10/10 to.

Here is why. Plenty of products in those tests that don't win are actually preferred for sound quality. I have read enough instances and reading between the lines that the reviewers actually liked the unit that got 4 stars better than the test winner. The 352 sounds a little more like a brute force amplifier - it is - it is more capable of driving tougher loads but it can sound a little pushy while another amp may not have the overall power and drive but it sounds better on subtlety and fine detail - which to me is more important. Also, at the time of this review you posted the Rotel was at the end of its production run - it has now been replaced by a different model. Further, it is not just the amp but how it reacts with the speaker - Ie which amp is a better match for the Tannoy. It may be that the NAD is but I would try and listen to both. A lot NAD dealers here also seem to carry Rotel so maybe in your area they do as well.

The specs don't mean very much. An 80watt amp will provide a 3db gain in volume level over a 40watt amp. 3db is virtually inaudible and only when played at the very extreme volume levels would it be differentiated.

As for your question about 8ohms that is the nominal or average rating. Some speakers can dip down to under 4ohms usually in the bass and or treble. This requires an amp to double it's power (or more than double its power) during passages where content is at those frequencies. Speaker makers usually don't provide the info. Generally though 8ohm speakers rated at 8 ohms won't go below 4ohms so they're pretty easy on amps. But not always. All of those amps will likely be fine with most 87db sensitive 8 ohm speakers. Tannoy is generally pretty benign here as well which makes them desirable for lower powered amps.