I have one 24" iMac (18 months old) and two mac minis (brand new). Upon purchasing the two mac mini's for my kids I also I purchased external speakers for all 3 macs. All 3 sets of speakers were the regular one line (non USB) style of plug in line, and all gave me the same non-recognition problems, meaning, when I went to the sound settings on all 3 macs, it only was recognizing the internal speakers. However, when I bought my USB line speakers home from work, all 3 macs will recognize the USB line speakers. This is soooo weird. Any suggestions would be very much appreciated.