I went through this a year and half ago. I have a 2008 and it had the six disk and the navigation system. The navigation was out of date and the screen was scratched and dull, CD player ate the first disk I put in. So, started researching and went to local radio installer for advise. I went with the Kenwood DNR876S and the Garmin Navigation. Additionally I did have a back up camera installed. Although, it wasn't one of my needs the Kenwood came with a phone system and I do use it. The Garmin also has a number of things I wasn't looking for, elevations, road trips, gas mileage, etc.
I have the Shaker 500 speakers and they have worked fine with the radio and CD player. I did not go with a six CD player and haven't found it to be a problem. The backup camera came with quartz lighting so at night you can see great, daytime not as good and if the sun is behind you, worthless.
I'm over 82 so we could blame this on age but I'm pretty good with computers, etc. One mistake I made the Kenwood offered a moveable screen (up & down) that would have helped with the glare problem. (my 08 is a convertible so others may not have the problem)I find the Kenwood overly complicated, that is, sometimes instead of just one step to affect a change it requires several.
Hope this is some help.