technical question

my brother-in-law has a problem. He has an Adcom amp/preamp (the amp is a giant thing, like 200 watts/channel). These are driving medium sized tannoy speakers. About 2 weeks ago, one of the tannoys failed, smelling awful as it blew. He was told that the woofer blew by a local repairman. In these speakers, the tweeter sits in the middle of the woofer. So, 2 weeks later while using his single remaining speaker, the same thing happened to the other speaker. It began to smell and then the sound faded away. Now I imagine that this means that the problem is the amp. Just to note, while I was there during the failing of the second speaker, we were listening at fairly low levels. Also, there were no pops or exploding sounds, just the fading away of the music plus that terrible smell. What is wrong here? Where does the problem lie? thanks in advance, david.