OK, so I'm assuming you are using the circuit I inlined above. Make sure it's the version 2 where the IBus line is pulled up. Otherwise the original circuit pulled up the IBus line with DTR. If DTR wasn't active, the whole IBus would be pulled down and wouldn't work (hence the first question).

1) Does the CD changer still work OK with your interface? It should.

2) Are you sure you have your serial port pinouts right? Looking into the connector male and female are the opposite. Usually the connectors have very tiny numbers printed on them. This is looking into a male connector.

3) Are you using 9600 baud, 8 data bits, 1 stop bit, even parity (8E1) and NOT 8N1?

4) What are you using to capture? I highly recommend Serial Watcher here for debugging this sort of stuff. It lets you select hexadecimal mode for non printable characters.

5) If you have a good macro camera, take some hires close ups of your board and I can have a look for you. My email address is in my profile and I can accept big emails.

6) When you have the changer connected, you are actually using it right (changing tracks etc)? Otherwise you'll simply get the hello messages every fixed interval. I thought it was 30 seconds but it doesn't matter.