Anyway, I bought 2 pairs (4 total) JVC 2-way 150w speakers for about $50 a pair. Unzipped each head rest, and had to cut out a section of foam on either side.

Each speaker literally just sits in there now, with being held at the back magnetised onto the steel brace up the back of the seat.
Oh .. and also, when you unzip, and fold down the headrest material, there will be a plastic-y mould that can be slipped out. I tried to keep it there, but the headrest wouldn't zip back up with the speakers that sit a little proud compared to normal. But even without the plastic mould there, it still looks fine.

Works a charm
