Product: Sonus Faber Concertino Domus Bookshelf Speakers; w/ Stands

@OP Harbeth and Spendor tend to fit that bill well - musical, neutral and not amplifier fussy. US prices are dearer than europe so basically anything from the Spendor Classic line or the Harbeth P3 or M30. The P3 is bigger sounding than its size suggests.

Why a power amp to mate with the NAD M33 integrated amp?

If you have the "curved" fancy stands with the slots/grooves on the front they retailed for $700.

DeKay

I believe that the extra power will result in a better quality sound.

Thank you for the info re the stands!

You just bought Sonus Faber speakers, now you need another pair of bookshelf ones?

I have the Concertino Domus as well as a pair of Harbeth P3ESR.  I enjoy them both for different reasons.  The Domus is no slouch and, not being sealed, trades off tightness of bass for more but bloomier bass, if that works in your situation.  The Domus is a thoroughly enjoyable speaker, super smooth and beguiling in the midrange, not really neutral, somewhat rolled off, but warm and engaging.

At the end of the day if forced to choose, I'd go with the P3 because to my ear the Domus doesn't quite pull off the magic trick of the P3s - which are detailed without being overly analytical and just about perfect in the midrange.  But for what the Domus cost, it's a very nice speaker.

As with all things audio, your mileage (and ears) may vary.  Enjoy them!