As evidenced by the answers in this thread there is no way to know. There is probably a slim chance you can review both yourself in your own system to compare I would wager?
Having said that I then went and looked up this Astell & Kern thingy. That little portable player is how much?
Going to ramble on with some of my thoughts:
You can stream with that little portable A&K thingy, or you can stream with something like my streamer, which has a mass of 42 lbs. Logically how could this little thingy serve up files with the same sonic clarity as a huge dedicated box with 2 computers and massive power supply capabilities?
Using the same logic, the Nagra is also a dedicated box designed to just do the same thing: serve/stream music files, so I don't think the A&K thingy has a chance to sound as good. The Nagra streamer is just 4 lbs- but that doesn't include the outboard power supply- is that a wal wart? notably one can upgrade its power supply- no idea how much that is and it is probably so new there are no reviews of that. But if one just needs that: to stream using Tidal/Spotify connect that is a nice, small, discrete, and attractive looking streamer, (mine isn't as shelf friendly) it may be a great choice. Nagra has a stellar reputation for top notch sonics, and Swiss (like my DAC) made quality. One review I just glanced at puts it above Lumin U2 mini for sound quality, but is should as it is twice the money, and Huff is drooling over it, probably because with a good review he can keep their $30k DAC longer...
I don't know- there are plenty of great streamers for the same amount of money, and that is before upgrading the power supply $$$ but the possibility of upgrades is appealing.
End of rambling.
No doubt the DAVE will eclipse the HUGO TT2, but to answer your question: which will upgrade your sound quality more? my money is on the Nagra- without a doubt.