Got the fronts replaced
The new 5.25" Polk speakers for the fronts arrived today and I got right to work. Changed out one speaker and did not move over the factory high-pass filter (bass blocker) to the new Polk and tried the sound alternating between the factory radio and the new Polk. I was amazed to not hear a huge difference between the two - I thought the factory speaker assembly sounded pretty darn good and the Polk was way too bassy.
Then I thought it would be better to move over the bass blocker to the Polk since I wanted it primarily for mid-range to highs. Installed the filter and tried another test (and did a little tweaking on the Pioneer head) and while not a humongous difference between the old and new, the new Polk did sound noticeably 'richer' - it is difficult to quantify the difference. The factory speaker sounded rather flat compared to the Polk. I thought the front speakers were 4x6 ovals, but my Rubi must have an upgraded sound system.
Installed the other Polk speaker and made another test and there is a definite discernible difference between the old and new speakers. Having said that, the factory front speakers are pretty darn good considering their size, I think the air-tight enclosure is an immense help for the sound of the little guys. The Polk would undoubtedly sound much better with a similar enclosure.
This was another incremental improvement in the sound system. Too bad I don't have a magic switch to compare the original audio system (with the bad sub-woofer) to the new head, new Bazooka sub, and new Polks for the front speakers.
(Sorry about the picture quality - they are with my iPhone, I was too lazy to grab the Nikon)