Val,
I don't think that any headphone with higher than 100 ohm impedance will work satisfactorly with the CMOY amp. You may want to rethink your choice if that is the amp that you are set upon.
As to sound preferences, I try to call them as I see them. You may like most types of music, but are you looking for sweet vocals, a recessed, flat or forward midrange. Do you favour violins over vocals?, string instruments over brass?, drums over triangles?, pianos over synthesizers?, etc. And how "forward" do you like the midrange? Others look to delicacy in their instruments, or decay in bells, etc. Bass isn't the end all if it is boomy or flabby, or if it isn't in a good proportion to the rest of the sound spectrum. It's all a matter of personal taste. Some people want the bass to extend to 20 Hz, while others like the bass impact of Grados. Every headphone therefore has their own colouration, some more than others, others less than most.
The fact that you are in MA. means that you may be able to hook up with DarkWolf, and perhaps meet up at their next meeting. There are also meetings in CT. Although if you're in the western part of MA, ie, "The Pines", you may have to try to find a Head-Fi'er in Albany, NY.
The DT770 has an impedance of 600 ohms, minimum. A beefier amp is therefore called for. The DT770 calls for a lot of voltage - voltage that the op amp may not be able to provide; it may clip a lot, causing massive distortion. As it is, the DT770 tends to have a darker sound, which to me means missing highs, transparency and decay. So you'll try to turn up the volume to hear the highs, which will in turn tend to exacerbate the problem.
A lot of people here tend to favour Meta42's. And the Antness Gilmore is highly though of, along with the RKV, and host of others. It all depends on your wallet.
You may want to consider a lower impedance headphone, perhaps one with more midrange to high end energy ( 2KHz to 5 KHz). It's a more "pleasing" sound to many, especially if you're into rock music. As it is, I'm afraid that your Nomad may be a bright source (as a lot of Creative products are) and therefore would tend to make the DT831 sound horrid, even more so the DT770.