And please notice that back at the time (2010 I guess) I did not even know really much about the importance of differential (balanced) needing to be 100% the same, while this light stuff - now I think of it - won't be "the same" at all. I recall that it even requires some means of calibration and that the leds will deviate from that over time.
http://www.tortugaaudio.com/products/ldr3x-v2-1/This guy claims he is "approaching" 99.9% accuracy from his LDR modules ( target attenuation vs actual measured), and he has an auto-calibrate feature since the LED do deviate over time. Still, that's not to say he has solved the fundamental issues that LDR's may have.
Regarding the need for "investigation," I agree of course. No doubt I'm limited by my knowledge and lesser experience, which is why I like hearing from others with more of both. I will say that a huge reason why a disproportionate amount of my audio budget goes to Phasure is that your (Peter's) standards are simply higher than everyone elses.
Should Phasure release an outboard attenuator, I'll be first in line. I think that's the bottom line here
I don't mind forgetting about those other things in the meantime. My current solution (Benchmark DAC2) is certainly not ideal either, but at least it's already paid for and offers many other features besides.