I'm more or less in the same boat as you, i was also considering the Essence and the Musiland 02 (along with the Auzentech Forte and the Audinst dac/amp).
Just for you to know, most people who recommend the musiland over the essence limit their opinions to music and overall sound quality, but the Musiland does not bring Dolby Headphone (like the Essence), CMSS3D (like the Forte) or any other gaming routine. I may be wrong, but also, since it is an USB dac, you wont have the chance of fixing that in the future by adding a dedicated soundcard since you wont be able to connect the dac to the soundcard (again, i might be wrong in this one, i'm not sure if the double RCA-out in the back of the musiland is able to do that. In fact, i have my Pioneer bookshelf stereo system plugged to my pc with those cables and i use it as a perfectly capable amp).
About having "out-of-the-box" volume control, don't get complicated. My 10€ logitech keyboard has a wonderful volume control (wich in fact i use a lot more than the one in the Pioneer, wich increases volume but also noise). You don't need to waste 100€ in a dac/amp just to get volume control. There are also headphone extension cables with volume control on them (My old Sennheisers brought one, you could even modify the volume for the right and left channels separately).
I can't really help you with my findings since i'm stuck right now. I don't have the impression that the difference in audio quality is that big between the Musiland and the Essence (seems more like a matter of tastes than a real quality difference), but i don't really like the idea of the Musiland being USB (you can't "chain" future upgrades) and also not bringing any gaming routine. The Essence is repoted by most people to have a outstanding sound quality (that will do to me) and it brings Dolby Headphone. Btw it also has an onboard amplfiier.
I wonder if there is any (cheap) way to get CMSS3d working out of the Essence (by adding some hardware i presume). If thats the case, i think i would search no more and get that one. I find less feedback on the 2 dacs so i wont risk the money just based on (maybe biased) personal opinions.
* Oh, you can test Dolby Headphone in some sofware (like PowerDvd 10, or WinDvd for movies, and foobar2000 with some tweaking for music) and even plain youtube videos (look for Dolby Headphone test). I just can't find any way to get any software to make it working on games without dedicated hardware (looks like a marketing limit to me). I wonder if the STX drivers could work without any Asus soundcard installed (at least to add DH in games, since i can already use it in movies and music).