Yeah I already own a set of 5.1 THXs, I have had them for about 6 years and no problems. I think so long as you don't listen to them extensively at high volumes you won't have problems as the amp troubles always arose from overheating components in the sub. The 5.1 systems don't have potentiometer-based volume control either so it will never get scratchy.
Anyways I loaned my speakers to my cousin when I moved away because I did not have room to take them with me. I recently found a used set on ebay which I purchased because the seller was within driving distance (which cut away a lot of shipping costs) and while he owned a 5.1 Ultra sub, it was a warranty replacement given to him by Klipsch when his THX 5.1 sub went out. Thus the set I bought had 5.1 Ultra sub + control box and THX satellites. Was happy with this deal though as the 5.1 ultra sub and satellites were in perfect condition.
I called Klipsch and they told me that indeed the satellites are no longer available. The center channel is but not the satellites. No word on when or if they would ever get more. The stupid thing is that Klipsch's Canadian distributor still has replacement satellites but can't sell them to me because I'm in the US. But the US people don't have any and can't get them from the Canadian distributor? Really dumb-IMO. If the US distributor is not able to sell me the item because they don't have any, why can't the Canadian dealer break the policy and sell to me due to special circumstances? Guess they don't want my business???
I found someone selling a set of 5.1 ultra satellites on ebay recently too though so I have a complete set of 5.1 Ultras, and a spare set of 5.1 THX satellites