Just ordered a new MY13 Q3 TSFI -

Monsoon Grey
S-Line pack with Nappa Leather
Teknik Pack - Xenons, MMI plus etc
18" alloys

I'm thinking of upgrading the sound system, changing out the speakers and putting a sub under the seat, something like this -

TS-WX110A Space-saving Amplified Sub (150W) - Pioneer Car Speakers, Sub

Would be keen to hear from anyone else who's done this?