Would this work?
I don’t know, but it probably doesn’t have the filtering that the Isobar Ultra has. The Line Conditioner is probably overkill for what you’re experiencing, and since it has a rather large transformer in it, you may be introducing more problems (like EMI) into the scenario, compared to what you’re experiencing now. If the Isobar Ultra doesn’t fix your problem, it’s still a fantastic surge protector for your audio gear.
It’s also possible that there is some arcing taking place on the Rega power supply switch, and the arcing of this switch is reaching into audio frequency territory, which is broadcasting this signal as RFI. It’s possible the Schitt Mani was able to previously reject this noise, but the Lehmann Audio Black Box SE can’t.
My best suggestion is to try the very affordable Tripp Lite Isobar Ultra. It has eliminated so many pops and clicks (from home inductive appliances) that I was experiencing before, that I was never able to eliminate.