@Saunter - With my old expert there was a subtle but definite difference between using a source fed via USB and using AIR. AIR was good but when compared to a decent USB source there was a difference in the presentation of bass. With AIR the bass was more accurate and defined, but with USB the bass could sound a little fuller and richer. I always much preferred the bass VIA AIR rather than from any USB source, but some USB sources could certainly sound like they had more bass. In your original query, you do not mention bass at all, but you do say that with AIR the sound is "flat and a bit brittle sounding". So what I am wondering is that if you have switched from USB to AIR you might have experienced a very slight tonal switch due to a subjective loss of a little bass. The bass may be good now, but if it has lost a little in the tonal balance this could lead to the "brittle" sound that you mention. You said in an earlier post that you have the speaker positions optimized, but maybe when running AIR the positioning may need a bit of fine tuning, speakers a little nearer the walls or corners perhaps?
If you are running Devialet AIR via Ethernet, I do not think the power supply to the NUC will make much difference, in theory it should not make any difference as the Devialet takes the Ethernet feed and it is stored in a FIFO buffer, and the Devialet streams from the buffer. (you can remove the Ethernet cable and AIR will keep playing for a couple of seconds) I would certainly look elsewhere to find the issue before spending more cash. It might be worth trying running the Ethernet via a standard network switch, if the NUC is producing a little electrical noise, even a standard network switch can help to remove this and isolate the inevitably noisy NUC from the Devialet. (do you have a spare switch and Ethernet cable to hand?)
It is very hard to judge this stuff remotely, so I may be very wide of the mark with these thoughts, but you never know!
As a first experiment, I would try a fine tune of the speaker positions or maybe even tweak the bass up +2dB, just to try. If that doesn't redress the balance, then fair enough and time to look elsewhere.
EDIT: Another experiment you could try is running Devialet AIR from your laptop, this should sound more or less the same as AIR via the NUC, if it does not, then there is something strange going on. It might be worth a try, to at least eliminate any problems with the NUC as being the issue
If you are running Devialet AIR via Ethernet, I do not think the power supply to the NUC will make much difference, in theory it should not make any difference as the Devialet takes the Ethernet feed and it is stored in a FIFO buffer, and the Devialet streams from the buffer. (you can remove the Ethernet cable and AIR will keep playing for a couple of seconds) I would certainly look elsewhere to find the issue before spending more cash. It might be worth trying running the Ethernet via a standard network switch, if the NUC is producing a little electrical noise, even a standard network switch can help to remove this and isolate the inevitably noisy NUC from the Devialet. (do you have a spare switch and Ethernet cable to hand?)
It is very hard to judge this stuff remotely, so I may be very wide of the mark with these thoughts, but you never know!
As a first experiment, I would try a fine tune of the speaker positions or maybe even tweak the bass up +2dB, just to try. If that doesn't redress the balance, then fair enough and time to look elsewhere.
EDIT: Another experiment you could try is running Devialet AIR from your laptop, this should sound more or less the same as AIR via the NUC, if it does not, then there is something strange going on. It might be worth a try, to at least eliminate any problems with the NUC as being the issue
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