Every OPTO•DX is signal calibrated using a RIGOL DS1104Z oscilloscope and then tested on a benchtop listening setup consisting of a Hugo MScaler to OPTO•DX to Hugo2 to AQ Nighthawk headphones. I use a loop of reference tracks—that I know intimately—playing from a CD player via Toslink. Here i have paid zero attention to power RF isolation since i am just looking for convenient and functional power. This setup represents the worst case configuration (SQ wise) that an OPTO•DX user may have.
A secondary listening space allows for the more critical listening required to test & compare power, cabling and misc RF isolation and product tweaks. Here i do pay attention to power isolation and use a higher end headphone (Stellia's traded in on HE1000se) for their increased resolution and transparency. I also test source configurations (Roon + HQPlayer) to ensure that any software revisions are fully tested - Windows, Mac and Linux (Ubuntu).