Just for the record, BBE should have never been introduced in a car audio environment. What it's intended purpose is for is to "enhance" the sound in a loudspeaker environment, ie a club or concert setting. It does nothing for bass, but it cleans up the mids and highs. A true BBE processor has about 10 different settings to it for shaping the sound. As far as your problem, when you had the factory HU in, the line level adapters are really kinda crappy, and most of them have some sort of gain setting on them. You more than likely were overdriving your subs when you switched to true pre-outs and henceforth the loss of sound. If you have an external EQ or x-over then definitely keep the BBE off. I'm pretty sure the JVC decks have a dedicated sub out which doesn't get any of the feed from the BBE process at all. If you have more than one amp in your system make sure you run your sub amp to that output. As far as adjusting you high/mid/low settings on the deck, it doesn't make much of a difference unless you run a multi amp system since all of your speakers will see the same signal. If you have an EQ or x-over then you are seperating your sound to different amp/speakers and can hear a difference when you make the finite adjustments to the different settings. Hope this all helps....