Upgrading the 8000's to SE is your biggest gain in sound quality. It is also the biggest expense. Upgrading the v6 to v8 is the next biggest benefit with LPS etc.

The DSP420 channels can have delay added in order to compensate for EBA in the 8kSE. The DSP520 will do EBA natively so they would make for a nice blend with the front end.

I would say that updating the center channel would be a bigger benefit than the 420/520 sides. Other opinions may vary.

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