Paul
you are currently set up as a 3 channel system. The front speaker should really only be one channel and the sound bar in the back is stereo therefore 2 channels.
good idea to dump the soundbar as I've heard from various people it's not the best sounding unit.
Yolu really only need 2 GOOD channels of music and preferably in the front. The idea of the kickpanels is your best idea by far. I wasn't aware of any for the C2's that handles a 6.5" speaker but if so than so much better but most likely mounting depth may be an issue on better quality speakers. Also, to put speakers in the kickpanels, expecially a 5.25" or 6.5" you are probably going to have to lose functionality of the fresh air vents....... is this something you are willing to lose?
IF ( a big IF since i know you a little bit from all our posts) you are willing to lose functionality of the vents, and you can get good kinkpanels to hold a good quality speaker in a 5.25" or 6.5" size to fit there than I'd definitely go that route and pick up a decent 2-channel amp to run the speakers. The radio may be rated 50 x 4 watts but believe me, it's really not - that's a peak power rating and your real power rating is somewhere around 12-15 watts per channel - not even close to run the speakers loud enough to overcome road and engine noise in our C2's and not drive the little built in amp into distortion levels.
Kick panels with good speakers and a good quality amp with a continious power rating (RMS power) in the range of 50-60 watts/channel will make a world of difference in your car and you won't even need to worry about the dash center speaker or having 4 channels instead of "only" 2 channels.
2 channels of very good sounds is MUCH better than 3 or 4 channels of poor quality sound.
*EDIT: ok, you posted just before I did. Even if the dash speaker is set up with dual cones and voice coils to be 2-channels, since they are so close together it really makes no difference practically speaking over the original mono speaker in the dash. There is no seperation for a stereo effect.
My suggestion to you above still applies