So from everything I've read, it'* a ROYAL pita to replace the stock head-unit without screwing up all manner of things. And I don't really have a problem with the stock head unit. Is it possible to put in aftermarker speakers and an amp to drive them without replacing the head unit? Not really interested in running a sub.

Sure is.

First off, we need to know your budget, as budget dictates mods. In any event, you will need at the very least a low-level converter to convert your speaker signal to a lower voltage amplifier signal. Shop around...there are tons of them out there, and the more expensive ones even have eq settings.

Next up is the amp or amps. A 4-channel amp will do ok, but if you are going to be running component speakers, you would be better off with separate amplifiers.

Speakers. Don't skimp on these...esp. the rears. If you do not wish to run a sub, but still would like some punch, high-quality 6x9s will be the ticket.

Ebay is your best friend in cases like this. Many shops have discontinued merchandise that is still new but at much lower cost.

I've done an aftermarket system before, just didn't know if I could hook all the aftermarket stuff up to the factory Monsoon headunit. In any case, a 4-channel amp wouldn't work anyways, right? There'* 8 channels. 2 tweeters, 2 in the front doors, 2 in the back doors, and 2 on the rear deck. Last car with an aftermarket system had uhhh... Pioneer headunit, Clarion 4-channel amp, and Boston Acoustic speakers. It was a small 91 Prelude, so it only had 2 fronts and 2 rears.

On another note, my all-stock Monsoon system currently has a nice background hum... very soft, but very annoying. Any ideas?

This is not correct. The head unit sends line level signals to the Monsoon amp. Just replace the amp and speakers. All the wiring can be used (unless you are going to high power outputs - and it doesn't sound like you are) so it is pretty simple.

A four channel amp is EXACTLY what you need. The Monsoon amp is a four channel amp. The amp is in the trunk behind the rear seat. It is a direct swap, front and rear channels in and front and rear channels out. I can get the wiring info if you need it. The speakers will use crossovers for the tweeters etc.

That hum you mention MAY go away with the new setup but if it doesn't, it can be a real PITA!

I am in the process of a similar upgrade.

He didn't state it was Monsoon in the first post, hence my statement of the LLC.

I've looked in the trunk a couple of times and never really seen an amp back there... maybe I'll need to look closer. In any case, I still don't see how a 4-channel amp can drive 8 speakers? :?:

Each channel drives TWO speakers and there is a crossover to direct the signal to the appropriate speaker.

Ahhh, well, in any case.... where is the amp supposed to be in the trunk? Is it hidden behind a panel of some sort? I looked back there and didn't see anything.

The amp is located in the trunk. You'll find a plastic panel that spans the width of the trunk immediately behind where the rear seat back is located. Remove this panel. It will be held in place by one clip towards the upper right side, the remaining fasteners are magnets across the top. You'll find two diagonal cross braces. The amp is located on the driver side brace and should be labelled "Monsoon" in red lettering.

Edit:
In reference to the factory head unit, there are four outputs connected to the input of the amplifier. LF, LR, RF and RR. The head unit will adjust the output level based upon whether there is an amplifier detected (there is an amp present signal in the wiring harness).

The Monsoon amp has the following outputs:

L & R Tweeter Output (Front Door)
L & R Front Midrange Output (Front Door Panel)
L & R Rear Speaker Output (Rear Door)
L & R Subwoofer Output (Rear Shelf)

In the Non-Monsoon, 6 speaker systems, the two front door speakers are wired in parallel (within the door panel) and there are no rear door speakers. This leaves LF, LR, RF and RR connections directly to the head unit.

I don't have the same year or trim package as you so I am going by memory. I believe the amp is mounted to the framework that is the back of the back seat. In my car there is a plastic cover over the area.

EDIT:
It looks like this is redundant - ddalder and I posted at the same time