The most common problem with using USB as a source was always that it was also commonly used to supply power. I remember seeing one piece where this was lauded as a great solution because only one lead was required. I felt like screaming "what about the feckin' noise it creates in the signal path" but after many years of verbally abusing a series of televisions, I guessed I'd get no more response out of a Chromebook, so restrained myself.
The problem seems to have been recognised, and in a large part, remedied now. Indeed, one major factor in my buying a Tinker Board was precisely this reason. Although it's powered via MicroUSB its four USB 2 ports are completely separate. The other little bonus is that you don't need a "specialist" case for it as you're not going to be using a "HAT" so any bog-standard Raspberry Pi case will fit. This also means, of course, that although the Tinker Board is more expensive than a Pi you don't need to buy a HAT to interface between the TB and your external DAC. Another plus is that it's a bit speedier than the Pi, and has Gigabit Ethernet which helps exploit that speed when using Volumio. The UI is very responsive and indexing my two Synology NASs was appreciably faster.
At the moment it's approaching the quality I had from my Pi/Digi+ Pro but I'm leaning towards believing that my choice of USB cable might be flawed. Reviews state that it takes quite a while to come on song, so I'll persevere for a while longer. The bass appears to have firmed up and it's more musical than seismological now, but the top end still sounds very brittle to me.
On the whole though, for around £120.00 for Tinker Board, case, MicroSD, and USB cable, it's proving a worthwhile experiment, and I haven't even tried out the onboard 192K/24bit output yet.
Next, though, I need to find out which bits of code to hack around, The Pi has a nice little config.txt file which allows you to add code that will disable things like the unused (by me) HDMI subsystem, and actually throttle back some processor tasks. The Tinker Board, sadly, does not. Looks like I'll be spending some time trolling Tinker Board forums, and asking silly questions.
