As a result of this thread I have placed the following in my E53:
Dash Midrange: Memphis Audio PRX275 (4 Ohm?????)
Front A-Pillar Tweeter: JL Audio C2-075-ct (4 ohm)
Front Door Woofer: C2-600 (4 ohm)
Rear Door Woofer: Dayton Audio RS150-4 6" (4 Ohm)
Rear Door Midrange Position: JL Audio C2-075-ct (4 ohm)
I am very pleased with the sound quality upgrade running through my Eonon GA6166 HU. Nothing has blown up and I gave it a thorough 1200 mile shakedown cruise just after the speaker installs.
Based on how WOW'd I am with the Vifa/Peerless mids in my E46, I am ever so gently considering putting them in the E53 rear door positions.
When I get back to the E53 I'm going to sit in the back and listen intently to determine if I'd like a stronger mid range back there.
As I experienced first hand with the 8ohm Founteks in a previously 3 ohm factory position, the higher impedance/resistance knocks down the effective volume one hears from the higher impedance speaker. Assuming moderate power inputs, I would not think any damage to amplifiers would occur. BWTHDIK????
I am now thoroughly enjoying my E46 GM5150 Eonon HU. Once I heard what was possible in the E53, I cringed at the sound of my E46 factory 15 year old HK speakers.
This has been a great speaker upgrade thread and thanks to everyone for contributing their research and experiences.
Stay tuned.
Mike