There are a number of common questions asked on the subs & sounds subforum and many of the answers are in the following posts...

1. Head unit recommendations:
http://www.elementownersclub.com/forums/viewtopic.php?t=1445

2. Jumping into car audio in the Element:
http://www.elementownersclub.com/forums/viewtopic.php?t=2115

3. Adapting Aftermarket Head Units to Factory EX Systems:
http://www.elementownersclub.com/forums/viewtopic.php?t=2636

4. List of speakers that work in the factory openings...
http://www.elementownersclub.com/forums/viewtopic.php?t=2692

5. What are coaxial and component speakers?
http://www.elementownersclub.com/forums/viewtopic.php?t=2926

6. Aftermarket Navigation System Installed (with pictures):
http://www.elementownersclub.com/forums/viewtopic.php?t=945

7. Satellite Radio Discussion:
http://www.elementownersclub.com/forums/viewtopic.php?t=2108

8. eMass's audio system (with pictures & diagram)
http://www.elementownersclub.com/forums/viewtopic.php?t=1488

9. Element Audio System Integration Wiring Diagram:
http://www.elementownersclub.com/forums/viewtopic.php?t=3276

10. Where to install component crossovers in the Element:
http://www.elementownersclub.com/forums/viewtopic.php?t=2444

11. Aftermarket car alarms and installer recommendations:
http://www.elementownersclub.com/forums/viewtopic.php?t=2354

12. JL Audio Stealthbox (replacement subwoofer) for Element:
http://www.elementownersclub.com/forums/viewtopic.php?t=1673

13. Useful Element Electrical System Wiring Information:
http://www.elementownersclub.com/forums/viewtopic.php?t=1540

14. Honda Amplfier Vs. Aftermarket Amplifiers:
http://www.elementownersclub.com/forums/viewtopic.php?t=1263

15. How to turn off the door chimes so radio can play:
http://www.elementownersclub.com/forums/viewtopic.php?t=3266

16. Subwoofer discussion:
http://www.elementownersclub.com/forums/viewtopic.php?t=3235

17. Newbie audio help discussion:
http://www.elementownersclub.com/forums/viewtopic.php?t=3173

18. ALPINE makes EX sub, sub enclosure, & speakers...
http://www.elementownersclub.com/forums/viewtopic.php?t=1576

Please take a look through these posts especially if you're new to this subforum.