Speaker and Head unit ????
 

I bought 4 new door, 2 new dash speakers and a new cd player for my 01 Blazer. I went to the local audio place and they told me to only install the 4 door speakers since the new cd player will only run the four speakers. Does this sound familiar to anyone out there or does this guy just not know what he's talking about? I have never heard of anything like this and when I've installed other cd players in my other vehicles they've always had and ran more than 4 speakers.

What they're saying is pseudo correct. All your speakers are likely 4ohm speakers. That is also the lowest rated impedance for 99% of the amplifiers that are built into the HU's. When you connect the speakers in parallel the HU amp will see a 2 ohm load which can cause it burn up very quickly, I've even seen it burn ground traces on the circuit boards before. A person could wire them in series, but you'd likely not be satisfied with the output as it will reduce the overall power output to the speakers, but you wouldn't have to worry about damaging the HU's amp. If you really want to use all 6 speakers, I would hook the dash and rear door speakers up to the HU and get a small 2 channel amplifier to run the door speakers. That would be the best way to to it IMO.

Not sure about 01's, but my 96 has the dash and front doors split together as "front" and the read doors as rear.

I bypassed this and ran new wires to the dash for "front" and the front doors on are the "rear" now.

Never run speakers on the head unit period. Lower quality, less power and it just heats up the unit