Yikes. Well, so much for having music by xmas. 
But you should not have gotten a squeal, and there should be no ill effect if you do not hook up a speaker to an audio amp. If you still have everything sitting out, can you take some close-up photos of the wiring? I'm thinking I might be able to see something that I took for granted but I was not explicit about. Otherwise:
The definition of insanity is doing the same thing over and over again and expecting different results.
