Is there a huge difference between sound package plus and the standard radio? I have found a few used 997.1's without the option and wanted to make sure the stock radio was not terrible.

 

Yes there is a big difference, you should listen to both before making a decision.
You can always add rear speakers and an amp. to the standard sound system and end up with a similar or even better system. I have the upgraded system in my GT3 and it's acceptable at best. Based on the specs for the standard set up i think you will not be happy unless you don't plan on listening to much music.
Attached are the specs. for the standard and sound package plus systems.

 

if you plan to keep the stereo stock, yes it makes a huge difference. you'll have more bass and you actually get an extra 5" speaker on your door, its a completely different panel.

 

So Sound Package Plus has a separate amp, where is it located?

 

for the 997.1, it was located in the same plastic box for the DVD nav player.

 

Thanks, can't be any significant weight then.

 

here's a picture of the sound package plus amp (non bose). whats good about the non-bose amp is you can replace the amp with an after market amp and keep the oem pcm. the bose amps are all digital and at the time, i could not find any after market amps which could replace it. keep in mind that the analog amps (sound package plus) only works on the analog PCM's and vice versa.

 

Interesting... The 2010 with Nav & Sound + does not have the 2 compartments on the lower left. Must have done some tighter packaging. Thanks!

 

I have 2006 C4S w/non-Bose. Sound is less than impressive. Has anyone replaced the linear amp (located in DVD box) w/a more powerful aftermarket amp? If so, did it help? I would prefer not to lose the OEM PCM. Also, has anyone installed two subs in back firing up at rear glass? Some tight (not boomy) bass would be nice. At present it seems nearly non-existent.

 

You can upgrade the audio system in the car without changing the OEM PCM. There is just more involved then just adding an amplifier. From what I remember in designing systems for C4Ss adding any media/audio into the fiber optic loop will require additional hardware to make the audio function properly. A common setup that’s sounds great is using a signal sound processor, amplifier, and “single sub”. I would go with a single 10” or 8” sub customized into the back to save space. Plus, they make very shallow subs now that work very affectively and produce great low frequencies (you never need 2, well not in a hatch). The signal processor is what you would need to retain your OEM PCM and control/tune your sound properly. With those three Items there will automatically be a dramatic difference already and you could move these 3 items to every car from now on. Last, just add a great set of front components 3-ways or 2-ways and that system with the right person to tune your processor will blow your mind! Hope this helps!