this guy usually has Upgraded rear speakers on ebay
http://search.ebay.com/_W0QQsassZsales4pnpartsQQhtZ-1QQfrppZ50QQfsopZ1QQfsooZ1QQrdZ0?
he didn't went I checked it out, but he will prolly repost soon. They are something like $220 and go where the stock ones went. They are supposed to be better than stock as well.
Also, you can opt to ditch the entire rear storage cabinet and have custom boxes made for speakers behind the seats.
Hope this helps
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