Some further impressions:
Got my HD555s on Friday, so I had something decent to use for comparisons. I also picked up an Asus Xonar U3 (basically a Xonar DG crammed into a USB stick) as a semi-impulse buy, so I'll be doing a little comparison between that and the E10 as well.
First off, the 555s make a huge difference in comparing my laptop's integrated sound to the E10. I sort of alluded to this earlier in the thread when I compared my IEMs to my crappy headset, but the Sennheisers confirm it. The 555s also have very little hiss, much less than my GR07s. It's barely audible at max volume and high gain. Sound-wise, the synergy is nice and the bass boost makes a noticeable difference in the sound without muddying up the signature like it did with my old phones. It's doubly nice because the HD555s are a little lacking bass for certain types of music and the bass boost adds just the right amount. So, overall excellent pairing between the HD555 and the E10.
Comparing the E10 to the Xonar U3, things get a little tricky. Sound signature-wise, the U3 is a tad brighter and more transparent with a little more low end than the un-boosted E10. The quality of the sound is nearly equal, and it's taken quite a bit of listening to pick out the slight sound signature differences between the two, which is surprising given the price differential ($40 for the U3, $75 for the E10). Their main differences lie in their features. The U3 lacks the volume control, bass boost function, dedicated line-out jack, gain switch, and coax-out jack that the E10 sports, but it does have line-in capability (mic jack), a S/PDIF adapter, and a bunch of fun software goodies like Dolby Headphone that make it great for gaming and movies. I still haven't decided which one I prefer - the U3 fits my needs for gaming and movies to a tee and doesn't sacrifice much, if anything, in sound quality to achieve it. However, it lacks external volume control and doesn't have the juice to drive anything with much higher impedance than the HD555s. I can max out the volume on the Asus without hitting earsplitting levels and comfortable volume is somewhere around 60-70%, while with the E10, between 2 and 3 on low gain produces the same volume level. I also prefer the design of the E10. For now, I think I'm going to take the E10 to the office and use it on my work computer, which has an abysmal hissing problem - bad enough that I use my DAP all day rather than plugging into my computer there. If the FA-011s turn out to need more juice than the U3 can provide, I can always swap the two. Or take the Fischers to work...