The Luxury Collection of Sheraton has a nice quaint one in Salzburg..just can't remember the name as I am still jetlagged from my trip unfortunately. But it should be on their website.

Relais & Chateaux also have several nice ones in Austria.

Have fun!

PS: In Vienna, I like to stay at the Meridien, which is nice and light and so different from anywhere else in the city..good location too.