I have found both heaunits for really cheap prices. I have found a local, barely used alpine 9851 with three year warranty for $200 and a Kenwood X789 for $205 shipped from SonicElectronix.com.
Which has better sq/output?
Which is built with better quality(physically built)?
The only thing that worries me about the alpine is that it has 18watts x 4 rather and only 2volts pre-amp voltage compared to the kenwoods 22watts x 4 and 5v pre-amp voltage.
I plan on installing four 6.5 kicker, alpine, pioneer, etc aftermarket speakers in my car that will be powered by the headunit rather then a seperate amp.