Well car audio is about the only thing I have a decent understanding of when It comes to cars. I can't say too much about the six disc player you are talking about as I have no experience with it. The sony however, I have plenty to say but I'll stick to main points. Its not worth the money! There, I said it. Flame away. The components and stats of all sony head units are so completely, ridiculasly priced for what you are getting that the original 8- trac wouldn't be such a bad idea. Thats not to say sony is a bad product, its just that you could get the same quality out of a deck the sells for half as much. If you plan to have a system that sounds decent, at best, under lower loads the sony will do. If you plan to give it any kick, I would suggest something else. Pioneer has a decent product in that upper echelon of the low end market. If you really plan to do some thumpin, go for something better yet. My suggestion would be a clarion. They are better priced for what you get. Yes, they are more expensive, but the internals and base stats are better. Eclipse is better yet but they do not have a removable face plate so its easily seem by theives and your car becomes an easy target. Anyway, I guess I'm done with my anti-sony speach. Choose wisely, bad audio will ruin any ride.
If you want some more details/options, feel free to pm or e-mail me.