Watch those speakers as they are a funny fitment, if it's the same as my S3 they only have 3 screws to hold them in. You can get adapter rings from a guy in the UK on ebay. Hit me up if you need them and I'll find him again. Worth waiting 10days for something that fits perfectly. HE makes a sub box to replace the Bose factory one which is cool as.
Personally, I think you can get decent sound out of speakers in the factory positions and then have something better in the back.
Gavin
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