I am using a presonus audiobox usb going out to 2 yamaha hs50m monitors. When used on a laptop, with or without the power supply hooked up, i get no ground loop hum. When used on my desktop, i do have ground loop hum. I do not have the option of isolating the circuit because i live in a dorm. Would purhcasing an ebtech hum-x and plugging the desktop into it remove this ground loop hum or is the problem internal within the desktop? My desktop is much more powerful than my laptop so I dont have the option of using the laptop.
Can't you use the "ground lifter" adapter for the AC Power? Use it on the speaker's power supply first and see if that fixes it. I would prefer the speakers over using the ground lifter adapter on the PC.
An Ebtec may do the job, but the ground lifters are cheaper if they work.
The ebtech will be the safest and 'legal' route in case your studio burns down. A cheater plug is NOT a proper means of handling electricity and your insurance company will have a field day if they find it.