That wouldn't satisfy the need for a signal on the bus. That could take the place of using a manual source selector (it's an auto source selector) by toggling power to the remote turn on terminals. Like I said in an earlier post, you could use an XA-30 which is basically the same as the XA-300 minus the USB (which you don't need anyway)...I've seen those several times on Ebay over the past month for around $20-30. The XA-30 would take care of the bus signal *and* provide you with the aux in that you need. Personally, I'd buy that and then later on add a CD changer if you still want/need one.
Try www.autoleads.co.uk, they make all sorts of leads for head units etc.
I recently e-mailed there tech support with exactly the same question and was told to get part number PC7-100.
I don't know the cost or whether it is available internationaly but e-mail them and ask.
Above is a BRL50.00 (USD$20) solution that I've found for me. It's simple, hidden, and works. You might find something like that in the US too.
I have a Sony head unit with this bus system and I AM NEVER BUYING A SONY PRODUCT AGAIN.
Leave it to sony to take something that should be compatible with any stereo signal and make it a proprietary connection. They went out of their way to do this to force us to buy more Sony products.
I am an audio engineer and everyone I know asks me for recommendations on audio equipment and I will never recommend sony anything to anyone. The only reason I even have the unit is because it came with my used car.
This is typical of Sony:
Remember their first MP3 player? It didn't play mp3s, it played sony's proprietary ATRAC3 format in an attempt to curb music copying.
How about the Sony BMG copy protection scandal of 2005? Where they manufactured audio CDs that installed malicious software on unsuspecting customer's computers, again to curb copying.
How about memory stick? The SD card is widely used and compatible with the largest number of devices, yet sony uses the inconvenient memory stick to extract a few more dollars from you.
I just noticed lots of dealers on ebay sell a $10 dongle that tricks the head unit into thinking a cd changer is plugged in. Just search for "sony unilink" on ebay.