I believe the Shaker & Shaker Pro systems have a 'box component' type of speaker in the doors, and not the flat 'plate type' as shown in the base model here. That's why there has been discussion on finding and ordering mounting brackets for replacement aftermarket component speakers.
Eventually I want to replace the 6x8's up front with these; C5-525 - Car Audio - Evolution® - C5 - Component Systems - JL Audio
I have a set of GT door panels that had Shaker 8" speakers, and will add a pair of these; 8W3v3-4 - Car Audio - Subwoofer Drivers - W3v3 - JL Audio
provided they aren't too deep, otherwise will have to go with; 8W1v2-4 - Car Audio - Subwoofer Drivers - W1v2 - JL Audio
Coupled with an Alpine amp, should be one hell of an upgrade... Alpine Electronics of America, Inc.