As the OP of this thread I would like to thank all of you for the help you have given. Since I posted the thread, I have had a chance to listen to the Avantgarde Duo's. In a couple of weeks I will be flying to Sydney to listen to the Acapella's.
I lugged by heavy Cary 805AE monoblock's to the dealer to have a listen. I was very impressed with the but with a couple of caveats.
Firstly, the dealer was unable to find a bass setting that made me happy. Either too boomy, or too hollow, or too little or too much. He told me that it takes quite a bit of time to set them up and i'm sure he's right.
Secondly, the horns do not integrate well unless you have the luxury of a large room and you can sit far away from them. Just walking back from the horns, I can hear them just about to start to come together at about 2m. 3m is better, but at 4m they sounded fantastic. The trouble is, I don't have that much space in my listening room. They would have to be flat up against the wall and that introduces its own problems.
Thirdly, the soundstage projected was too tall and not wide enough. I experimented with toe-in which cured the width issues somewhat, but I think the speakers had to be placed further apart than where the dealer had them (1.5m apart). I mentioned to my friend that it was like watching a movie with the wrong aspect ratio.
Apart from these caveats, the speaker really impressed me. I liked the easy sound, the incredible dynamics, and the subtlety they are capable of. I think that all the above concerns of mine would disappear with the "right" listening room and careful setup. Unless the Acapella's in Sydney do better, I will be looking at buying a pair of these speakers.