Poor bass performance from stock keenwood headunit.

[Woody_NZ]

Has anyone had any experience with the likes of this http://www.crutchfield.com/p_161LC2IB/A ... Black.html.

I'm using the stock headunit, 05 waggon, silver kenwood one, and i find it clips the low frequency bass.
I have upgrade the speakers all round to alpine and treble and mid's sound real good. I also have them running through a pioneer 4 ch amp so they have plenty of power and a 12 sub in the back.
low volumes sound good, full bass but the bass volume doesn't increase with the rest of it, so when i turn it up i'm over powered with treble.
I would rather no go down the road of those $600 fit kits and a normal heading as 1 they are stupid expensive and i like they way the stock heading looks its fits nice in the dash and the fit kit's look nasty.
this is why i'm thinking i need something like whats in the link above. or if anyone has another idea I'm listening.
Thanks