Go to an audio shop and get some decent rear speakers installed! I can guarantee you it will be much less than R1500! Pioneer, Kenwood or something. MB Quartz, boston, Hertz and those speakers might be worth it if you're an audio nut

If you go that route I would also replace the front speakers (and tweeters) as they are the ones you listen to most

Hmmm looks like I'm getting carried away, maybe I should get myself a new pair of speakers

Audi A3 1.8T
ex "BroSpeed" RXi