I am sorry for being so late with the Hydra-Z (H-Z) impressions.
The main reasons are that during the test, there are so many parameters that changed, so it was hard to do sensible comparisons.
I removed my preamp and went direct from the DAC to my amps and then I got a new preamp and have tweaked sensitivity and gain stages ever since. I have also updated firmware on several sources in that period   - I guess you get the messsage.
But anyway, the impressions I got is that the sound from the H-Z is extremely clean. Maybe on the verge of being tight and slightly anemic in the bass region when going direct with no preamp. However with a preamp in the loop there is increased bloom that matches it very well. The funny thing is that the USB output of the Aries actually feels quite warm (maybe tightened up a little on the latest updates). For those who think the Aries USB output is too soft, I can assure you that the H-Z compensates for this. Note that it was only the I2s output towards the DirectStream that was used during the test.
I have a hard time believing that you can have a source with a more expressive sound in the treble and precence area without being overpronounced or aggressive. You get a feeling that every sound is released from your speakers and I can tell you there is absolutely no sign of muffled sound. Still, I would say that a preamp brings more ‘foot tapping’ enjoyment into the listening session, especially during prolonged listening at higher volumes.
So, to summarize the biggest difference from going Aries USB direct is similar to going from the PWD MKII to the DS. The sound is tighten up and the bass is more articulated. The difference in perspective, imaging, soundscape, timbre, etc is not that noticable at first listening, but the sound reproduction is extremely distinct.
I plan to have some HIFI buddies in for a listening soon. When I visit others, I really miss my sound…
The technical aspects with the H-Z has been virtually flawless so far. I am running it passively powered from the Aries.
There are no latency or pops or clicks of any kinds that seem to origin from the H-Z itself or the result of hooking it up.
More impressions to follow later…