Oh boy oh boy!
Hope its amp can one-up the Quickstep!
The only reason to go for the UHA760 would be for its additional features as there doesn't seem to be any difference in maximum power output between the two. Most likely you can expect the same performance in terms of that. However, high gain on the MKII is +18dB (8x) while it on the UHA760 is +12dB (4x) so if you're needing to dial the volume pot way up to drive your DT990s even in high gain, you would definitely want to have the gain on the UHA760 adjusted.
As I'm quite happy with the MKII at the moment, I'll also be waiting for impressions. Hopefully someone will be able to compare it to the MKII and tell us if signal upsampling and the improved power supply brings noticeable audible improvement. Also would like to see pics of the PCB :D
If it's a $100 upgrade by trading in my uha-6s mkii, i'd do it. I never use the leckerton as a dac, but maybe the dac performance may be improved a little so that it's actually worth using.
Edit: for the version with optical and coax inputs, not the standard one.
One-up the Quickstep for SQ? We will see about that. Nonetheless the size, features and DAC could make the UHA760 very attractive.