Went back to work today, I have an hour commute so I finally got a chance to crank up the volume a bit. I know this is the IA forum so a bit for me might seem miniscule for some. The biggest subwoofer system I have had in a vehicle was two SA-12's with 1200 watts in an Expedition, which was great BTW.
I have a stock head unit with a JL Audio FiX-82 providing the signal to my amplifiers. I was playing a notch below my clipping level using a 50 HZ test tone. I am giving the subwoofer around 550 watts. The Flatlyne sounds good. It will play every note you send it. I listen to almost every music genre and this sub sounds great.
I have posted here that this sub is not terribly loud, but my ears are hurting from my drive home. You have to consider the fact that it is a 15 in a hatchback, so I would rather err on the side of being "too loud" and just being able to turn it down.
I wish I had better command of the English language to describe how it just fills my car with this awesome bass that just hugs you and makes you happy.
Great product plus great customer support, you just can't loose.