There are two schools of thought on this question & perhaps Dave will eventually weigh in with his own advice.

The first belief is that rear fill speakers are not really necessary, especially in the rather tight confines of the Contour's interior. If it was a dimensionally larger vehicle, say a Lincoln Town Car, station wagon or SUV then rear fill might provide a "fuller", more enveloping, 3-dimensional sound stage.

However, it is possible for rear fill speakers to negatively impact the overall music reproduction by pulling the sound stage rearward if the system is not adjusted properly. This phenomenon results in an unnatural sound as the music seems to be coming from behind the primary listening position instead of in front of it.

Frankly, if you like the way it sounds in it's current configuration, why change it?

If you absolutely want to retain your Eclipse speakers, then by all means either run your a/d/s/ amp in full four-channel mode or better yet, utilize the internal amplifier on your head unit for the rear fill & either bridge your four channels to power the front a/d/s/ speakers as you described in option #2 or distribute them between the tweeters & mid-woofers as in option #1.

In my own system with the P840.2 amp, I bridged channels 1 through 4 in pairs for the front speakers, channels 5 & 6 power each of my Boston rear fill speakers & channels 7 & 8 are bridged to power my single Infinity sub.

1999 SVT Contour, #2140 of 2760, Tropic Green - Medium Prairie Tan
Koni Sport struts; TSW Blade wheels; Nakamichi, a/d/s/, Boston Acoustics, Infinity I.C.E.

1989 Saleen Mustang, #89-0408, too many mods to list here