09/10 second gen with Monsoon sound system, upgrade info

[Th17kit]

I spent a fair amount of time searching this forum for information on modifying the audio system in the 09 and 10 models with the Monsoon stereo system. I haven't found much, and definitely nothing in an organized post, so I'll post my questions here.

While I'm impressed with the stock Monsoon sound system in my '09, it does have its drawbacks. First, the knobs come loose. Secondly, there aren't many features that an aftermarket deck can provide, like bluetooth, USB, SD card, rear aux etc. Third, the aux in port, while convenient, doesn't have the same power level as the tuner or CD, which leads to shockingly loud mode changes if I forget to turn down the volume before switching. This third problem bugs me the most, because I understand that distortion is most prevalent when devices are near their maximum output, which both my cell phone and stereo are if I want loud music.

Let's keep this simple, if possible. I imagine many of us are interested in upgrading, but don't have much expertise. I don't have any experience with pulling car doors apart/laying wires in cars. The extent of my experience is replacing the head unit in my '96 Honda Accord.

Some background: Info on sound systems in cars including premium features: http://www.edmunds.com/car-technology/c ... stems.html and this is useful for understanding where to start with upgrading: http://www.edmunds.com/car-technology/c ... o-add.html

Great wiring schematic of the '09/'10 sound system: viewtopic.php?f=18&t=40537&p=478921&hil ... on#p478921

So, on to the questions:

Is the 09/10 Monsoon system essentially unchanged from the previous Moons & tunes Monsoon systems? If so then viewtopic.php?f=11&t=40421&p=478825&hil ... on#p478825 this DIY will be incredibly useful.

How is the Metra 95-8224 dash kit? I've read about some fitment issues, in particular the kit fits the dash well, but is ~6.7" wide instead of 7". Have people had good/bad experiences with it?

Is replacing the head unit as simple as getting the dash kit, an aftermarket HU, and the wiring harness?
Did this improve the sound quality?
Has anyone found an inexpensive way to incorporate the Onstar (so I mean other than the $150 kit), or better yet use the microphone in the RV mirror for bluetooth calls with or without cannibalizing the Onstar?

Has anyone replaced the sub without replacing the amp? Did you find an improvement in bass reproduction?

Has anyone replaced the amp while leaving the OEM wiring? Did this improve sound quality?

Ultimately: What are the most effective/efficient upgrades for this system? I was taken aback that replacing the HU alone won't add any power to the system, unless you rewire the speakers. It just seems like a potentially gigantic amount of work!
I'm sure there will be more questions - I'll try to update this post as time goes on.

[Th17kit]

From user jmkcc

I started by changing the door speakers and the tweeters along with a Pioneer FH-X700BT head unit. I was going to keep the factory amp - but there was a slight hiss which I figured was because mismatch with the HU and amp. I ended up adding a Pioneer GM-D8604 4 channel amp. I tried running a separate cheap boss mono amp for the subwoofer, but it did nto work so well. So right now I am running the 4 doors and two tweeters off the new amp and will add a subwoofer amp at some point. This will probably mean repalcing the OEM subwoofer which is 2 ohm, dual voice coil, 40 or 50 watt. Sound great now, I'm using Infinity 629I 225W speakers that I got on Amazon for 75 per pair.

In hindsight, I would have saved up for a 5 channel amp, although I'm not sure you could find one that would fit under the passanger seat. I think there may be some room under the back seat for a subwoofer amp, but I have not pulled it apart yety.