For music or HT...both?
For music, you might try the Thiels, NHT's, or other "matter of fact sounding speakers". The Mac's are forgiving and sweet on top. I think you'd be happy in this genre. Anything with that "transparent, uncolored, detailed sound" should do well. I can think of speakers like Maggies, Thiels, Wilson, Apogee, NHT's music line(not as refined ultimately), Talon, B&W Matrix 805's for cheap to Silver Sig's, Proac 2.5's, etc.
I would stay away from Sonus Faber, Mirage, Vandersteen, and other warmish and or veilied sounding speakers.
Otherwise, Macintosh's own speakers work well with those amps obviously. Good luck