The one thing I like to use this for is when I only have my iPhone with me. Then using BT, this allows me to make/receive calls when necessary.

Yep, it is kind of an overgrow BT headset that will work with your supply of headphone.

Looks like the E3 digital volume is not independent of the computer volume settings, unlike the E1?  I set my E1 volume around 50% and control the volume through my keyboard buttons.  I can see how if the E1 was always set to 100%, I'd have to keep the computer volume pretty low to keep things comfortable, depending on the sensitivity of the headphone.

@Sam L You should have kept your PC's volume relative high and control the volume on E1, that way you will be getting the best dynamic out of the system. While digital volume is definitely easy to use, it does eat away your bit depth when you are lowering the volume. Lowering digital volume too much and SQ will suffer.

@ClieOS I thought that since I'm feeding into the E1 via usb that I didn't need to run the signal out of my computer as high as I would via 3.5mm jack?

You'll always want to set the volume on your source higher to ensure you are getting the best quality signal, for both digital and analog control. Remember that you won't get all the 24bit bit depth out of a 24bit DAC (a really good one will give you around 20bit or so effective bit depth), so it is best to keep the digital volume high enough so you are at least getting a full 16bit.

Well creative tells nothing about the output power in mWatt for their headphone ampilifers. Same issue with the THD details. IMHO creative just jumped on the headphone-train and tries to make some money. Yes, i had sereral creative products but after some major problems with their warranty politics (back in 2009), i'm pretty rigorous with their stuff.

@ClieOS Got it.  I didn't know that with regard to a digital source the volume needed to be at max whenever possible.  Makes sense though as you explain it.  Am I correct in assuming the quality of an analog signal is more effected by volume than digital (ie. tos link, usb, etc.).