Take a look on what this adapter of DDHifi is doing on the scheme. It does not touch any signal lines of the amp, but the line which in normal case is supposed to be a shield of the balanced cable as you say. In my understanding this shield is provided by basically providing ground (“zero level”) signal of the amp to the physical “shield layer” of the cable composition.
But in case of the adapter you would be using SE cable anyway, so there is no shield layer - the ground is provided to the zero line basically making the connection single ended. The problem would be if in the amp section the “0” of L balanced and “0” level of R balanced would not be matched creating channel misbalance.
That pinout you provided working means the iFi amps are ground-referenced and built in such a way, they can work in a “half-balanced” mode.
If I can find a non-working/for parts iFi amp on ebay, I will take a good look inside to understand what the hell they are doing.
The problem would be tieing R+&L+ or R-&L- together, because then playing a tone on Left and Right with a 180° phase shift between the channels would short them out (minus output impedance of the amp).
You are trying to plug single ended gear into something that only has a balanced connector. I suppose I can see that being an issue. That gets me to what piece of gear are you using that is creating this problem for you?
I live in the budget end of things, but I rarely see amps that only have balanced connections. Gear with only one connector tends to be 3.5mm SE, or XLR. With XLR only, you just get the XLR adapter with the connector you want ( or wire one yourself ). Those don’t seem to be the case for your setup, so I am curious.
My FMR RNC 1773 is single ended, and will throw a mild tantrum if fed +10dB level. So Cleanbox it is!
The connection between my el-cheapo mixer and audio interface is balanced (because 5 meter cables through the room with headphone “returning” to the action running along side them). Depending on what I am doing on the input side of the mixer, I use the 1773 as a “master compressor” before the audio interface.
