Seems an odd upgrade, the RCD 300 is fine and the car has at least 8 if
not
10 speakers, mine has 10 working but on the MKiv forum there is talk of
the
2006 model only having 8, I have had my Golf since March and have no
worries
about the standard radio set up, I have seen pics of the facia adaptor
with
a head unit fitted , the combination certainley spoils the look of the
interior, personally for the cost of another HU, money maybe better spent
on
options like an ipod adaptor or the phatnoise which was under 200ukp.

Personal preference I suppose, but I found the RCD 300 to be rubbish, drove
me crazy after 3/4 days. Base was ok but mid-range and tonal quality were
terrible, cheap and nasty. IMO money spent on an Alpine or similar is VERY
well spent, and if you get the right set up it will look good and of course
you can hang on to the original (you wouldn't get more than £20 on eBay for
it anyway) and refit it before selling. The speakers on the other hand seem
well up to the job for everyday use.
Regards
Martin