Any update on this ?

Yancy, Stangbat, have you checked the schematics ?

CGC indeed changed the original midrange + tweeter configuration to two cheap midrange. But they left the capacitor of the original design on the right side !??

tweeter_(resized).png

Yancy, I'm about to switch to full range car speakers too. I want to crimp a 4-wire Molex dongle to convert the parallel configuration to serial, to be able to switch back easily to 8 ohm speakers later if I need to.

I plan to wire GRA-ORN to GRA-BLK, GRA-RED to GRA-RED and leave GRA-BLK alone.

Signal would leave the board from SPKL (J6 pin 5), go to GRA-RED, enter the left speaker, go to the right speaker through GRA-BLK, and go back to the board ground through GRA-ORN -> dongle swap -> GRA-BLK (J6 pin 4).

Is that what you did ?

Ok thanks, it ends up being the same wiring.
Good thing you used the GRA-RED instead of GRA-ORN if there's indeed a capacitor on the right side (weird).

Ok, speaker swap done. I installed 3-way coaxial car speakers.
The original uncompressed sound files now shine in all their glory.
All the voice calls are much much cleaner (the S, CH, F, X sounds are all better).

Like yancy said, any 5¼" coaxial car speakers of some recognisable brand will be an improvement.
The only thing to look for is the color. They are visible through the speaker grill so make sure you don't buy a model with funky colors (http://www.covingtoninnovations.com/michael/blog/0405/040507-SonySpeakers.jpg)