I checked this thread only today - as I have been interested in what did the measurements of iFi iDSD BE reveal. Interesting, to say the least.
But I do not respond because of anything concerning iFi. That grounding blues, experienced in (some?) Schiit units, is FAR more widespread than most people realize. Goes both for the new and vintage gear - the latter may, although working perfectly when new, well show such illneses with the passage of time.
The culprit is always down to the same two reasons: either anodized coat/oxidation between the parts hold together carrying the ground by screws or cold solder joints/joints made to heavily oxidized metal in the first place. More rare are direct omissions of grounding wire(s), where everything has been manufactered to specs - but every one in a while, such devices do creep up.
I have seen many examples and combination of these in >40 years of my interest in audio. One thing is reading the assembly instructions - and another is double-checking everything is as it should have been. I will illustrate this on the most trivial example possible - soldering a wire to the RCA jack. On low end "silver shiny" plugs, the oxidation layer ( which is there to prevent "rusting away" of contact surfaces ) can be so thick that simply soldering just won't stick to its surface. One has to get to the BARE metal first - and solder to that definitely not oxidized portions of the plug. The best tool to do this is glass pencil eraser, when not available, any fine small file will do the trick. With gold plated RCAs, this is (usually) not an issue.
But most RCAs, regardless if low end or gold plated in the lower price brackets, have the ground connection part actually made from two separate parts, which are then crimped together. And here usually the problem lurks. If you connect your RCAs "once in a lifetime/year" - very few insert/disconnect cycles - it might work just fine. If you for any reason have to do it more frequently, that supposedly zero ohms impedance from the ground collar of the RCA plug and its spade the ground wire is soldered to can become intermittent - or even open circuit, no matter how you "wiggle" the offending RCA connection.
For that reason, I grew a habit of actually soldering over the joint of these two potentially problematic pieces - and, if done correctly, they never gave that problem anymore.
Above has one, but big fly in the ointment for the manufacturer - it takes MUCH more time to prep and solder RCAs as described above than simple "bussines as usual". And time equals money - we all know what thatmeans in this highly competitive world...
The same applies to assembling an amp ( perticularly problematic if it is "natural metal color" - for which we ASSUME it has conductive surface(s) , when in reality ic can be heavily anodized electrically non-conducting ) - or even superficially as benign item as phono cartridge headshell. There are many cases the screwing the parts together or crimping are expected to cut trough that non conductive layer, thus establishing the required ground connection - but more often than not, the parts joined together in such a fashion DO NOT CONDUCT ELECTRICITY.
I have seen this in new equipment that misbehaved one way or another due to the lack of proper grounding. The only proper way is to disasemble such piece of equipment and figure out where the ground connection between parts screwed together should be - and physically remove the paint in the vicinity of the screw(s) required. One can spare the trouble of disassembly by using an external wire to the chassis part(s) - but it is not the proper solution.
These ground screwed together joints can and do exidize in vintage equipment - again, disassemble, remove any oxyde ( sometimes cotton Q-tip is enough - BOTH on the bolt and various "holes" that ultimately make the contact ) - any you are good to go for another decade or so.
One nagging issue with phono cartridge headshells that should but do not conduct ( resulting in hum, nomatterwhat ) is the fact that they are crimped together and can not be dissasembled in a non destructive way. For those, I use the following technique :
1. Remove a small portion of anodization ( coloured or transparent ) in a remote area out of the usual sight that does bridge all the parts that should be conducting but aren't. You have to get to the bare metal.
2. Apply with a small brush silver lacquer/paint sold to repair heating coils in the back window of cars ( off ebay, etc ) to the spot with the paint removed. All this can be say 2 x1 milimeter in size.
3. First, after 2. dries, double check with an ohm meter the headshell now is conducting properly (0,0x ohms and lower ). Then apply some brilliant transparent acryl lacquer/paint over the silver lacquer, to prevent any further degradation of conductivity.
In a perfect world, the end customer should not have to deal with issues of grounding described above. But, since we do live in a real world, one that is far from perfect, we have to take into account that any of the remedies described above can be more time consuming than assembling the entire product in the factory.