Hi all, twas bluepilot that done a write up on splicing into the speakers. I did it a few weeks ago, what I found was that the main loom has a 100mm ish cable's running of to each speaker, like you say there is not much room. I took both of the cables off, laid the Starcom cable on the floor and spliced the two cables on the ends of the cable and soldered them when they had cooled I insulated them and fitted them back in poking them up through the drain tube on the speaker housing before connecting to the speakers, worked a treat.
The other end of the cable that plugs into the intercom is just like a normal 3.5mm male jack so you could plug it in to any music do da I would think.
Roger