Thought I'd post up a mod I did to my wife's Symphony II so that it has a USB, SD card and Line in through the cassette slot.
The CD player was shagged when I got the car, so I got her a Connects 2 kit that has a box with s USB /Line in and SD slot - it hijacks the loom at the back of the stereo and pretends to be a CD changer - so you can play modern devices through the standard Bose system.
I got the box and was going to fit it behind the head unit with trailing leads to plug in, but then you can't use the SD slot.
It then occurred to me that the box was about the same shape as a cassette and perhaps I could mount it inside the head unit rather than outside.
So I removed the CD player from the head unit shell and then did the same with the cassette deck (they just have ribbon cables you can pull-out.
I then had to file down the plastic around the nice new Connects 2 box (and the hole thru the PCB for the cassette).
I've posted up the pics below of the process.
It was actually quite easy - and it's held in place by just being a bloody tight fit.
Now I have a bang-tidy install that looks completely standard, apart from the USB poking out of the head unit.
One word of caution - you have to file the slot for the cassette deck - the actual PCB - by a millimetre or so. Be careful not to take too much off. I left a small sliver of PCB before I got to the solder tracks above/below the slot - otherwise the metal case of the Connects 2 box could, in theory, bridge the connections.
You just keep filing-away until it fits - it's pretty tight though and can be very tricky to remove once in place.
Think I also had to 'adjust' some of the metal cage at the front slightly, and I put some rubber padding on the underside of the connects 2 box incase it came in contact with the PCB below it when mounted in position.
Hope someone finds this useful.