Crutchfield doesn't have any compatibility info in for the S550 yet. I've been keeping an eye out. I'm tempted to email them and ask when they plan to have it in the database.
You're not still using the rear channel signal for the sub, are you? I imagine that would amplify (poor choice of words) the problem. I feel like every factory system I've ever worked with has suffered from dramatic bass roll-off in the rear channel, especially at higher volumes.
I see on your site it says that the intake will preserve the sound tube interface. Will there be a cap included for those who would rather eliminate it entirely?
So, just spitballing here (another base audio GT).
Right now, I have an amp and sub in the shed from a previous job. I'm thinking I'll go ahead and install those now, and drive only the sub with the amplifier, then pick up replacement door and rear deck speakers down the road when I decide...
It depends on the manufacturer and the car. Chrysler seems to bring out competitive vehicles more than most. They had a few for their 200 refresh short-leads back in 2011, and I believe they're doing the same with their current round for the new car.
Media vehicles for first-drive events are...