Update: My research tells me that Bluetooth APT-X is the best sonic quality out there at the moment. I'm going to try this device first, and tell you how it goes:
KAC-M1824BT | Marine | CAR ENTERTAINMENT | KENWOOD USA
It's an APT-X Bluetooth amplifier that you can run directly to speakers. You can bridge it as well, to 90W x 2. That with some integrated separates and a compact sub should make a nice stealthy system. I'm still curious about door panel treatments to "hide" the speakers. Anyone?