Don't get me wrong, the Excelons sounded great when it came to highs and mids on the stock radio. They lost all the bottom end though.
I would like to keep some low end in the system without having to add an amp. The highs and mids will be dramatically improved with upgraded components and coaxials, but I don't want to have to add an amp or an amp+sub to bring the low end back.
I know SQ is subjective, but what I'm looking for is a speaker upgrade that will sound good with the stock HU and not require an amp...basically speakers that can handle the output of the stock HU.
OK here's the thing: The Kenwoods will sound fantastic, but at 20-22 as you said you were playing your stock ones at, your going to be clipping the HU and gettign distortion regardless of what speaker you install. This is why every install shop will say that speaker will sound much better on an amp then on a HU. Running a 30W MAX / channel HU will barely half-power the Excelons too. Sure you will have the ability to turn up the bass, and that's where you'll hear the thumping in the doors, which once deadened will actually sound much better. The other issue that I can't address because I haven't listened to the Scion's HU is it's cross-over path as the volume increases.
Many OEM HU's have a protection feature built in that prevents low frequencies from being output at high volumes, effectively it's a variable low cut. As volumes goes up, bass goes down. The Forte HU is very interesting as it'll let you put the bass up, turn on the power-bass feature and crank it. The distortion you are hearing is actually coming from the Amps, and it's not the speakers, as you can even hear it at lower volumes.
As i said above, I have my amps set so that 13 is really HOT coming out of the output side of the amps. It's a very clean signal in the 10-15 range, even with Powerbass on. But, as I said, the HU will clip above that with powerbass at full.
I did a little experiment today on the way in to work, to try and prove a point. I disconnected my sub(s) RCA's. I turned up Jamiroquai's "Canned Heat" quite loud and if you are familiar with the song, you'll know there's a big freq. sweep at the beginning, and a nice rolling bass-line throughout the song, along with a nice Kickdrum on every beat. Since I'm running JL C-5's in a set of sound-deadened doors on a 75W RMS 1-4ohm amp, (300/4 JL Slash series) I had no issue turning the bass up to 5, with powerbass off and everything else set flat and having a very nice mid-bass / bass sound. My crossover on the amp is set to about 72Hz so it will obviously not hit 30Hz at any percievable volume, however that's what subs are for.
As I said above, if you add a set of C-5's, or Focal K2's perhaps R series Aplines but I really believe they are need a sub to get low, so X-series would be what you would want, and Kenwood X's can perform if the door is deadened. A friend of mine here in Toronto Apecio from the kia-forums Forte section just recently installed JBL GTO's (Coax's in the front, and the installer diasy chained the factory tweeter off of them, and gave me a listen. They sounded really really good !!!!! I said, "you didn't tell me you put a sub in, he said, it's not in the car today! I said Bullsh1T! open your trunk... and low and behold, there wasn't a sub. JBL's are notious for being able to handle a ton of peak power and choke down disortion-like noise. This is probably why the make the best 6.75" components on the market : JBL 660GTi 6-3/4" Component Systems Car Speakers Car Audio Car Audio, Video, & GPS Navigation - Sonic Electronix
Anways, I'm not really familiar with the following lines to offer e-pinions:
Hertz, Rockford Fosgate
And I've demo'd every futureshop/bestbuy brand:
Infinity: Overrated power specs, wimpy
MTX: Wasn't happy with any of them
Pioneer/Sony/JVC: Alpine S Series counterparts. (Except the Pioneer Premiere line)
Energy:Alpine R- series -ish but not quite there.
My biggest recommendation for anyone finding that the cabin interior's plastic is contributing to a harsher sound, would be to try a couple things (should also help metal-dome tweeters sound a little warmer):
1: Deadening the doors will help pull the mids down, tighten the low-end and prevent a nasal sound.
2: If you find your tweets harsh, try adding a layer of light-velvet or other "soft" semi cushy fabric in front of the tweets and behind the trim panel to buffer the sound a bit.