Here's my .02
The GM Delco head unit isn't that bad actually. Unless you are going to spend a considerable amount of cash on an upper end unit, you're going to have a hard time beating it. Middle of the road head units (IE: 300-500 bucks-ish) aren't going to be a huge step up in sound quality, if any at all.
Have a look here:
http://www.davidnavone.com/heresHow/files/OEM vs Aftermarket Decks21.pdf
Where the OEM deck really falls short is in accessories/options since it was built to perform certain specific functions as GM dictated.
No pre outs, no aux in (at least no the type we want), no amp remote turn on, etc.
Let me use my system as an example:
I occasionally listen to the radio and the rest is MP3 through my iphone. CD's are just a PITA in the truck for me so I don't have a CD player.
I use the OEM deck, a PA11-GM45 ipod interface, a David Navone R-NHL4 (copy) LOC, couple cheapy pioneer amps and a sony Xplode (more like explode
) 10"sub.
Let's start with the OEM Delco.
It's a cassette player deck in my truck. Yup, I said cassette player. It came with the truck but they also go pretty cheap. Thieves aren't going to bother with it either. As mentioned, it falls short in "options".
Because there are no "preouts", sound in the unit is routed through the internal amplifier assembly. All head units have a built in amp section of some sort or they wouldn't work at all without an external amp. The problem with head unit amps is they are small, tend to be cheap and introduce "noise" in the amplification process.
Pre outs allow you to bypass the built in amp section for cleaner sound to your external amps. Typically 1-3-ish volts on a cheap/middle line deck. More on this later.
Good news is the Delco amp section is fairly "clean". Not perfect, but good enough for all but the most demanding SQ freak in car audio IMHO.
The line level outs are both a good and bad thing.
Good thing you say? The higher line level voltage is not as subject to external noise on it's way to the amp.
Bad thing you say? Because it's post amp section in the head unit, the noise induced by the amp section is carried along in the signal and then the external amp amplifies both the audio and the noise.
The RCAs can do the same thing: any induced noise will be amplified by the amplifier. Induced noise on RCA lines is typical of poor installation practices and can usually be dealt with by doing a good/proper install.
This is where the R-RHL4 LOC comes in for my setup. The LOC steps it down to preout levels. Where the Navone one differs is that it is active rather than passive. There is some processing and then it steps it up to a 9V preout signal. this allows me to go to the RCA jacks on the amp.
The RCA jacks are preferred to the "line in" on amps because the line in is just a built in passive LOC in the amp. They tend to be cheaply built and are largely pointless for any decent sound. The RCAs bypass this circuit.
The other thing the LOC does is provide a remote amp turn on, triggered by the signal on the speaker line. You get your remote on signal and you avoid any "turn on thump"
I run the high level signal from the head unit to the LOC which is located right net to my amps. I get the high level resistance to induced noise from the HU to the amp and I get the RCA in I want.
Expensive? Nah, ten bucks. Seems Mr Navone either sourced it over seas or had it built there and the exact same thing is on ebay for ten bucks. He sells it for 30.
I retain the nice features of the OEM deck. The integration to the interior, the ability to use OEM steering wheel controls and the speed volume control.
I have steering wheel audio controls also, so those are retained. You can retain them with aftermarket decks also, but you needs additional adapters.
As mentioned, I don't use CDs. I use my iphone to take my music with me. So I use the PA11-GM45 interface to connect it to the OEM radio. It goes in place of the OEM slave CD plug in on the HU. It charges the iphone, it plays through the HU, and it allows me to control the iphone through the radio/steering wheel controls. Simple stuff like forward and back, playlists, random, scan, on the iphone but that's enough for me.
I also use my iphone for OBDII interface, Hands free, voice texting, gps nav, etc. But that's another story.
The PA11-gm45 also has aux in ports for things that are not an iphone.
It gets pretty much as good as an aftermarket radio for inputs. Chuck in a Delco CD player head unit if you still use CDs and you're nearly got it all.
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Between the LOC and the PA11-GM45, I've got about 140 bucks in the whole head unit.
