There is no substitute for a sub-woofer.
I have a basic system in my Car, Entry Level Pioneer MP3, Clarion SRS 1626 splits and a set of Eclipse 4-way 6x9's (Which I got on Special for $100)
No amp in sight. All off the Headunit. So It won't send you deaf but does sound better then stock (Since mounting the front Speakers on MDF instead of Plastic)

Today. I installed some OLD gear I had. Namely a 600W 8Gauge power kit with RCA's and a Old 400W Jensen amp and an old 12 inch Ported Magnat Subwoofer.

All I can say is.. Wow.
Now I set the Gains on the Amp to low, I am not setting it up to shake the booty (lid) but to give the system some low end punch..

15 mins to install and run the wires to the boot. next 20 mins level setting the system so it sounds smooth, not over powered..
The deck I have has no subout so I had to level set it so the sub complements the 6x9's not over power them.. Lucky the old amp has a variable cross over built in..

The biggest pain in the whole install... Getting the remote and the RCA's into the head unit..

So to those who say 6x9's and subs don't work... They can... If you set the Subwoofer to cover the frequencies the 6x9's miss.. Which in a Magna, Seems to be alot..

Nice,
I've pulled an amped, 4 channel system, 6x9's and splits out of the 380, had it like that (ampless) for a week.
Now running a Pioneer Deck, 380 GT Fronts, 6x9's and a I added a a small Amp and 12"... Man what a Difference.

I know where you are coming from, that fuller sound makes a system....
Only problem is the center stage is about where the cabin light is.... Oh well....

mmm... Might install a set of Mids into an Enclosure behind the Headunit... nah... too much effort.