If you look at the prices brochure, RCD300 has 8 speakers, RCD500 has 10 speakers.
True, but the RCD500 comes as two options: either with - or without the Soundpack. GTI/R32 option prices for the RCD500, without soundpack is £275, and with soundpack is £675.
You can also get dealer supplied speaker "upgrade kits", the fronts (1K0 051 608 A) for £180, and the rears (1K0 051 606) for £115.
I have asked my stealer for the exact spec of these kits, but they are unable to tell me, and as Illy stated, Matt had a real run-in with VW UK on just how sh!te the soundpack was, and eventually got his money back!