[Empeg-ice] 6.5" woofers - useful?

[pim@empegbbs-noreply.merlins.org]

Now that I've spent a lot of money on my Empeg, an amp (Clarion CPA 4202) and installation costs,
I feel I need to spend some more on speakers, as these are now by far the weakest link in the chain.

My Alfa 156 comes with 6 speakers; 6.5" compo's in the front door, 6.5" fullrange in the rear doors.
Ihave already made an appointment to have the front speakers replaced with a pair of Canton CS 2.16
compo's.

Now I'm considering what to put in the rear doors. As I am reluctant to have any kind of sub in my trunk,
and because there's almost never anyone on the backseat, I was thinking of having just  bass
in the rear doors, using 6.5" (16.5 cm) woofers, which usually are labelled as "kick bass".

Examples are Kenwood KFC-W1703 and the Phonocar range of 6.5" woofers.
These speakers are relatively cheap, compared to compo's and coax speakers,
but also are high-quality if I am inclined to believe test magazines like Autohifi and Car & Hifi.

Now I know car-hifi freaks use kick bass speakers to fill the gap in frequency range between front speakers and subs.
Would it be advisable to use them as substitute for subwoofers?
My amp has a builtin variable low-pass filter (50 ~ 200 Hz, -12 dB/oct.).
Is that adequate for these kind of speakers, or am I better off with a passive filter using a higher frequency?
Or would I be better off using the woofer of a compo, and ditch the tweeter?

My installer recommends putting coax speakers in the rear doors, but I thank that's a waste of
(a lot of) money on mediocre sound quality.

What do you think?

Thanks,
Pim (60GB, red)