I had a Pioneer DEH-10 in my 70 GS. Thats a 1999 base pioneer model from wal mart. Sounded alright even after 5 years, but it wasnt cutting it with the new speakers and all. I did some research on the new Pioneer players with the OEL display since it looks so cool and all. Here is what i found.
Pioneer began using the display setup in '02 or '03. It is available beginning with the 6*** series players such as the 6400-6600(this years model), and is used on the 7,8,and 9 series.
These all use at least 2 pairs of RCA preouts for easy amplification with the later models having 6 preouts, with the extra 2 being used for the subwoofer.
The voltage output of these RCA preouts plays a role in the quality of the sound signal that the amplifier puts out, since it determines signal strength from the head unit to the amplifier. Generally the higher the preout voltage the better if your planning on using amps with your sound system.
Pioneer uses 4 volt preouts on most of these models which is about on par with most other higher end stereos out there. However for this year with the *600 series, they have downgraded so to speak, using 2 volt preouts on all models.
Also with the 2004 models like the 6600 - 8600 they have decided to remove the feature that allows one to add in their own animated graphics and screen savers to the display. This is a nice function that lets you put in pictures of your car, and you can even create animations with your pictures and videos. The new models no longer have this feature, which kinda sucks too.
Pioneer has a seperate line of products that they dub the "Premier" line. These are basically the same units with a "premier" logo instead of pioneer, and up until 2004 they have used 6 volt preouts instead of 4 like the pioneer models which is a plus. Also i have heard that the internals are better quality, although i cant tell you if thats true or not.
Basically if your looking at those models, then take a look for last years model instead since its got a couple better features.
I purchased a Pioneer Premier DEH750mp--which is the premier version of the 7500. Grand total came to 164 bucks off of ebay, compared to 300 for the new 7600 that you find in stores. Thats half the price, and more stereo for the money. Just an idea.