Thanks brother, I'm surprised more people aren't watching this and learning to adjust their gear, maybe they doing what I used to do, connect and go! Ha!
I'd say from experience tuning with the DD1+, tune subs to 0dB-3dB IF: - Your amp/sub wattage isn't matched, as in amp rating > sub rating, because clipping when the amp is overpowered is worse than clipping when matched Tune subs to -5dB IF: - The wattage is matched and impedance rise is known - You play rebassed music - You'd like a bit more oompf out of your system Tune subs to -10dB IF: - The wattage again, is matched and impedance/box rise is known and calculated for - You don't play rebasses, just regular music - You have a good working nose haha, subs give off signals when they're being clipped. Now for the mids and highs I usually tune to 0dB or -3dB on customer systems since that balances both clipping and loudness, as long as they keep the EQ as I've set them and only go in the negative section on the EQ and not positive, they'll be fine. -5dB for mids and highs when the vehicle/system might compete. Just my two cents, anyone can add or correct me if I said something wrong, just giving info that's worked for me.