The Harbeth 40.1 is perhaps one of the finest stand-mount speakers of all time, regardless of price. Unequaled midrange, awesome top-end extension that is completely fatigue-free, and a deep, rich bass response.
In medium sized rooms, you can get away with a good 20wpc amp or higher power (tube or SS). In a larger room and at louder volumes, at least 50wpc is recommended (again, tube or SS), and they certainly do not mind more power.
* This pair was specially modified by Harbeth USA (Fidelis) with Cardas rhodium binding posts, and removed metal hex grill on the tweeters for more openness and transparency. They are probably the best sounding 40.1s available! *