You have a selection of two very nice speakers! I have owned the AR9 and can speaker highly of the sound. I recapped and refinished the set I had. I also had the woofers rebuilt as the voice coils had sagged out of spec. Once rebuilt this was an outstanding speaker system, a true classic among enthusiast. Placement can be a bit fickle but when set up right is very good. You should use the AR9 with a minimum of 200 wpc, high current amp to get the best from them. Bi-amping is even better! They are quite an articulate and comanding speaker. Very enjoyable.
I looked into the Mac you also listed and read the lengthy engineers paper on them. They too look quite advanced with shorting rings used on the woofers, custom made drivers and complex networks. I would bet they do sound quite good as well. The one disturbing thing I saw was the low soinc output of only 84 db w/m! The AR9 was at least 90db as I recall. Bang for the buck the AR would play considerably louder for a given input! If the sound would be equal then the efficientcy would surely sway me here!
I have listen to many Mac XR series speakers and always found them very enjoyable, as I have many models of the AR series. Good luck with you choice and let your ears be your guide.
DC
