Pillar speaker replacement

I'm upgrading my speaker system in my 03 polo, I've already replaced the old, ripped original door speakers, but I'm having trouble both getting to and working out the size of the pillar speakers, and I was wondering if anyone could help me know how to get to them, and what size they are to replace?

Also, I've seen people talking about polo speakers all being part of a non-coaxial system, where once replaced simply by sticking in the new speakers onto the old wires, they stop working... This doesn't seem to be the case so far as I've just put my speaker cables into the polo adapter and they work fine, I'm just curious as I'm thinking of adding more, and if they are satellite speakers this will make it much easier.

Thanks