Yeap. I had a Mac MC225 connected to the Thiels 3.6. It sounded horrible! Ended up buying a VAC Ren 70/70. What a huge difference...
Before the Thiels, my Mac 225 was connected to a pair of Kefs and it sounded very nice. Not sure if I was doing something wrong, but what I can tell you was that as soon as the Ren 70/70 was connected in the system, it completely opened up the sound. Clear, natural, wide soundstage. Liked the VAC sound so much, that I have replaced my preamp with a VAC Ren Pre, too.
Due (and only to) to space constraints I might end up selling the Thiels. Otherwise, nothing to complain!
Good luck.