I have a music surround system for SACD and DVD-A that also does double duty for home theater. I am using 2 pairs of NHT 2.9 wirh and AC1 and NHT sub. All of the speakers were purchased at the same time in late 1999 or early 2000. All of the ID number say 1999. It is now 2010 and I was wondering if they wear out? They have never been knocked over anything like that and seem to work as well as the day I got them.