Gustard R26 ladder DAC sound signature - comments?

I'm evaluating a Gustard R26 while I can still return it to Amazon. I've been burning it in for four days now and did some critical listening both when I received it and just now.

I've heard great things about this DAC, including one guy who normally is interested in $10K+ DACs saying he was really taken by the R26.. extremely high resolution and very musical details.

My impression is contrary to that and I'm not sure my DAC is working properly. It actually refused to lock properly on the USB signal or make any sound for the first day, then suddenly started working.

My impression is that it's very dark and missing the top octave. For example, brass instruments (in classical music) are not brilliant or thrilling like I expect them to be. The highs are veiled and muddy. 

I'm comparing to a modded Gustard x20pro (this is a model from 6 years ago - in my case very highly modded and an excellent performer) and a PS Audio DirectStream DAC Mk 1. 

My USB transport is an Aurender N100. I have a very high performing USB cable and power cables custom from the same guy who modded my x20pro. The R26 is on vibration isolation. I'm using a custom 12AU7/FET headphone amp into LCD-2. Normally this system (cables, headphone amp, etc.) is very revealing of the highs. 

Can I get some other opinions on the R26? Is it dark and veiled to anyone else? And what are you comparing to, if anything? I wonder if mine is not performing correctly.