Aftermarket Sound/Nav: Yes or No?

[Toopskees]

First post. I am in the final stages of ordering my X5 and need some prompt advice.

Initially, I selected both the Technology Package and the Premium Sound Package. During my test drive, I noticed that the navigation system left a lot to be desired. For instance, I was driving on an expressway but the system kept telling me to "bear left" as if I were on the access road and it wanted me to enter the highway. Also, there was no indication as to what street I was currently driving on. After reading many posts in this and other forums, I learned that the BMW nav system is an inferior product.

The standard sound system in the test drive vehicle was barely adequate. They did not have a tester with Premium Sound, but I chose this option because I am somewhat of an audiophile. The additional power, extra speakers/subwoofer, and equalizer can only enhance the sound quality.

In all my previous vehicles, I have had custom-installed high end aftermarket systems. I have a friend who owns a local custom car stereo place, so I can get fairly good prices.

So here are my questions:

Should I take the easy way out and accept an inferior sound and nav system pre-installed at the factory, or go with a higher quality aftermarket system?

Does aftermarket equipment add anything to resale value?

Can an aftermarket system integrate with iDrive?

Would I be in jeopardy of voiding the warranty if I add aftermarket equipment and something else goes wrong?

Thanks in advance for your advice.