CTIrish

Hey guys! This forum is awesome. I love how helpful people are. I just bought a 2005 TL but it has some issues. Luckily I got it for a steal. Now to my questions.
The Navi system is reading "check disk." I followed another threads instructions on how to clean the cd lense, but that didn't fix it. I am not sure what I am going to do. I guess there isn't any way to just bypass it and still use the screen for the audio function. Does the Navi cause glitches in the radio/cd player as well? I loaded the changer last night and after 3 disks, the whole thing shut down. No function at all. Could not power off. I could only change the mode on the steering wheel, but 0 sound. When I shut the car turned off and back on, the radio functioned again. I cannot play CDs, though. I also hate that the only place that I can see the radio is in the heads up display where the a/c readout is.
I don't know what "normal" function is like, so I have no basis of comparison.
I have thought about putting in an aftermarket head unit, but have seen the issues that they can cause. Also can't find a kit to install it with. I know the strips that run down either side will cause issues on the appearance of the aftermarket head unit. I also don't want to drop the dough if it isn't going to work correctly. I need lots of help! Thanks in advance.