Glad your enjoying the wonders of Etymotics! Truly a remarkable experience when you first listen to music with Etys for the first time (and you have a good seal)! Like listening to your CD collection for the first time.
Now for the bad news... Since you're now hooked, enjoy the moment (that moment of pure audio bliss). Slowly but surely, you'll start to wonder what other phones might sound like.... and you'll end up trying them (FYI: very few can provide the detail and clarity that the ER4 provides, but other phones do have different properties that you might enjoy).
Slowly but surely, you'll end up looking for amps to improve the sound.
Slowly but surely, you'll start looking at your system and looking for weak points in the system.... new source, new interconnects, tubes, tweaks, portable system, main rig, bedroom system...
This viscious cycle never ends until you run out of money. Hence the traditional headfi greeting, "Welcome to Head-Fi! Sorry about your wallet."
Sorry. But, welcome to the (addiction) club!
When you're ready, definately should consider adding the S adapter cable. Just a simple cable (which can be removed just by unplugging) that adds a bit of resistance to the ER4P to make it the ER4S. The sound is AMAZING! Hard to imagine that such a simple addition can cause dramatic improvements in sound quality, but it does. Unfortunately, the added resistance means that you'll probably have to add an amp to make the ER4S really sing.
Congratulations!!
Bruce