I would be inclined to have a very close listen to the 66SE-KI with the 73. My gut feeling is you need a more powerful amp, good though the amp is. The speaker is pretty demanding, although the Pioneer A-400 is reputed to work well with it. The more control you have over that box, the better IMO and the AVLand deal for the Audiolab 8000S and 8000P amps for £349 and £299 respectively are well worth digging out and researching IMO.
The 60w of the "S" integrated for the tweeter and the 100w of the "P" for the drivers would be good. £549 on top of the cost of the speaker however.
Used, well, dave_k hit the nail on th ehead for me - the 75 series really sings with either good Arcam or Sansui amps (he referred to the 217, which I also have in addition to the current 717 amp) and you might, depending on budget, consider the Sharp Optonica SM-3636 amp currently on Ebay. Another dual mono design and it could be a bit of a winner I think. The Optonica range was very, very well regarded in its day, but the usual caveats for this, as well as all older gear obviously apply.