Upgrading the Pioneer System
 

After looking at the wiring on the 7 speaker Pioneer system, it seems to me the best option for me to upgrade the entire system is replacing the door speakers and subwoofer with better aftermarket units and putting in a 5 channel amp with a lot more power to replace the factory 5 channel amp. Has anyone else done this upgrade? Judging by the 20 AMP fuse that runs the circuit the factory amp runs on, I would say the RMS power of the factory amp is 15 watts to each speaker and maybe 50 watts to the subwoofer( around 100 watts RMS total, seems to be about right as Pioneer claims 240 watts max), so I was looking at going to 60 watts x 4 RMS and 150-200 x 1 RMS watts to the sub with an aftermarket 5 channel amp, which should more than be adequate for my needs. Anyone else who has done something like this, it would great for any wiring tips or install issues. My issue is I only want one amp in the car and it can't take up any cargo room, so I will more than likely be using the factory sub box and just putting in a better 8" sub.

Most 5 channel amps are huge, I was looking at them a while back. And the subwoofer section on those is usually class A/B. At the lower wattage you are considering, it may actually save space to use 2 smaller separate amps, and the separate sub amp would be a better class D.
There is a member here that used 2 small sony amps mounted next to the battery in the spare tire compartment, keeping all existing cargo space. Have a look down there and you will see there is a bit of usable space.

I have been looking at two amps, I was hoping to stay with one amp for simplicity sake but two amps would also work. I have found a few decent priced 5 channel amps that have an A/B amp for the 4 channel and the sub channel is a class D. It amazes me how far amplifier technology has come in the past 15 years or so.

if you are looking for small amps check out Arc Audio and 5 channel amps are the way to go for sure!

I have to make a point about people who have the Pioneer system and switch the head unit to an aftermarket unit and all then say the sound improved. It can't, the head unit doesn't even have speaker outputs, the sound is still coming from the factory amp. In the Pioneer system, the headunit is just a control unit and nothing more. That is why I have no problem with keeping it as it looks good and actually has a nice display and easy to use controls. It just seems weird that people think that changing this headunit will do anything to change the sound, it won't.

Well the sound will be louder most likely due to more high power input the amp recieves...is the unit really a "dead head unit" in the pioneer? Because I thought people were using the pioneer head units in regular LS and LT models without the premium sound just having to have the BCM reprogrammed.

All things being equal, that's true. The issue with a new head unit is that one now has the ability to tweak the sound even better for the existing car. So, better sound is definitely possible; however, as you mention, you are still sending the signals through the Pioneer amp and speakers.

I have to say, the stock Pioneer system isn't bad. In fact, I wouldn't touch it but for one thing....no Bluetooth (mine's a 2008). In addition, changing the HU gives me some options to tailor what I want in the vehicle. I've looked at some alternatives and decided to go with Pioneer's new AppRadio2 (compatible with Android, but a $100 kit is required, whereas Apple is compatible out of the box). With the correct adapter, I also keep all of the stock toys (amp, sub, XM, OnStar, etc.).

For anyone with an iPhone (only compatible with Apple products), the original AppRadio is down to $199 brand new at Best Buy right now...quite a savings.

I realize my HU will be tied to my phone, but I can't see a nicer choice for getting all the bells and whistles, including GPS on a 7" screen, for my application. After my HU is in, I'll then determine if I want to do anything with the amp and speakers.

As mentioned above, there are some small amps out there. I just got done replacing some older amps in my son's car. Space was a definite consideration. I went with the Sony Slimline XM-1S and XM-4S amps as the best option for me. Please don't think I am pushing anything....just what I decided on. These are some small amps that work well. I have them tied to Infinity Reference speakers and an Infinity 10" sub. They do a great job. These are the amps I am going to keep in mind for my HHR, as I hate visible equipment in the car.

I think someone on here already used those sony mini amps, mounted on the side of the spare tire well beside the battery.