Yeah please do! I am most interested in the 250 ohm 880/990 since they are the cheapest

I will probably need to upgrade my rig before going to the T90...
Sorry I couldn't get back to you on this the other day. I am testing out the uS on my DT900s right now. I'll report back with more impressions later, but I wanted to say that the sound is much better than I expected (not to say that I had low expectations, but I find the DT990s to be really fussy). I'll be comparing it with an Emotiva XDA-2 both as a DAC paired with a Schiit Magni and as a DAC/amp. I tend to prefer the DT990 paired with the XDA-2 /Magni combo. The Magni is a little brighter so it balances well with the bassy DT990s. With the uS, the balance is actually very nice.
Update:
This is probably going to require more work. I'm going back and forth between the uS and the XDA-2. There are very clear differences between the two but I'm finding it rather difficult to put my finger on what those differences really are. I want to try out different types of music, but thus far I've focused on two songs: Heaven for the Sinner (feat. Erykah Badu) from Bonobo's
The North Borders album (this is in 24/44.1 resolution, bought from bleep.com) and "Afro Blue" (feat. Erykah Badu) from Robert Glasper's
Black Radio (this is a lossless CD rip - BlueNote should really release a high rez. version of this album!). Why these? Because they are on my playlist and I know them well. My impression is that these songs sound better in general on the uS paired with the DT990s. However, the reason I don't use these headphones that much is because I find that they are a little boomy. That boominess is more pronounced through the uS than the XDA-2. For reasons I won't get into now, this makes no sense to me, so I've been checking configurations and computer settings to rule out other factors. At any rate, the uS also seems to bring the midrange forward where it is inexplicably recessed in the XDA-2. Booming bass aside, I actually prefer the combination of the DT990s and the uS to the DT990s and the XDA-2 -- not the result I expected.
Update 2:
I needed to spend much more time with the uS. What threw me was that the DT990s sound great through the uS but my Q701s sound a little thin. Considering the Qs are 62ohms and the the DT990s are are 250 ohm, the result should be the other way around. Nevertheless, after a week or two of going back and forth and trying various combinations (the uS through the Schiit Magni, for example), I'll say without reservation that the DT990s sound better than I've ever heard them straight through the uS. The most noticeable thing about this pairing is that the mids are much more forward. I've read that the uS does push the mids a bit and the DTs lack them a bit - this must account for the great sound. When the uS is connected to the Magni, the DTs don't fare so well. That midrange is not as powerful. I like to use the Magni for music that needs a bit of additional detail - bowed bass for example - so the weaker midrange is probably the result of the Magni's strength in the higher frequencies. I'd imagine that there are better pairings for the uS, but the Magni is all I have on hand.