Re: 6x8 recommendations - pioneer avh-2400bt HU - 07 focus zx3
With the small but nice selection of 6x8s on the market I say get 6x8s. They'll be louder than 6.5s and you won't need to buy adapter plates. Pioneer D-series are nice, and I like JBL as well. Once you get into 6x8 components the price jumps quite a bit, but you can step up to Alpine Type R coaxials for around $200 or less.
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