yeah.. that's not helpful to ME, as I already know what these things do and what they're for.
I realize that the oem headunit likely has equalization across it's high-level outputs.
But then, the same oem headunit also provides low-level, unaffected outputs rendering the need for this type of processor irrelevant.
Yes - your current, BMW OEM headunit, in your car right now, provides a pre-out for use with an amplifier as STANDARD
Finally, using any four-chan amp worth it's money, you can 'fudge' any remaining equalization issues by adjusting the gain for your bass, mid and high frequency band blocks.
So my questions are again this:
1: Why are you using line converters?
Your stereo already provides a low-level output and all you're doing is degrading the sound and spending money doing so
2: Why are you even considering a DSP?
Unless you're changing all of your speakers to high level components, spending money properly deadening the car interior, and buying a suitably high-quality amplifier (or two), I fail to see how you're ever going to get your money's worth from it?
I have an e85 with NO line converter, an Alpine PX-V9, the standard "carver" subs and "top hifi" speakers and tweeters - sounds great (not comp-spec by any means, but above and beyond OEM quality of any car I've personally been in).