There are certainly some differences between the units. What you are installing the unit into dictates which one you need.
First, there are the Non-Lux units. These require an external amplifier and will not work properly without one. You'll often see these installed in the Trail Blazer, H2, Suburban and several others. The amplifier in the vehicle must NOT be a class 2 amp. What I mean by this is that volume and other audio functions are handled in the head unit, not by way of class 2 data signals to the amplifier itself.
Next there are the Lux units. The vehicles which have these are usually higher end and will have the Y91 or Y92 RPO code. Because various audio functions are controlled by the amplifier directly over the class 2 data bus, these will not work with an amp such as those in the Bonneville.
Finally, and not very common is a version made for vehicles that do NOT have an external amplifier. I can try and find a part number for these. This type of unit would be perfect for installation in a Bonneville SE or SLE. Of course there are several other considerations to doing this.
Here is the thread relating to the install of my nav unit:
I also created an updated thread when I replaced the Delphi "aftermarket" version with a genuine OEM version. Here it is:
There are complete details, including parts to change the backlighting for the buttons and wiring harnesses for the adapter cable required.
*** YOU SHOULD NOT USE THE VIN RELEARN ON THE TECH 2 FOR THE BONNEVILLE TO INSTALL THESE UNITS ***
If you plan on doing this, I can provide details on how to perform this step.