Yet another need help with a ground hum thread

Hi all I am hoping that someone can help me out here. My sources are split between the living room and a small bedroom. I have a pair of Mackie monitors and a pair of SVS sb1000’s in the living room with a Schiit passive preamp and a Schiit mani DAC. I have my Technics SL 1200 in another room with a Icon Audio ps1 mkii. The turntable is in the other room to solve a feedback issue I was having. Upon first setting the turntable and preamp up I got an  immediate  ground hum. I tried the ground lift on the preamp and it didn’t help. The only thing that seemed to help was running an extension cord to the same outlet everything else was plugged into. I lived like this for a while until I could install an outlet on the same circuit thinking that would help. The circuit is run from the panel to a junction box where it splits to go to the living room and the room where the turntable and preamp are. Upon hookup the hum was back. The hum is present even when the preamp is not turned on. No idea what is going on with that. I have a super cheep Pyle phono preamp with a wallwart power supply I keep as a spare. With the Pyle hooked up no hum just a very slight buzz which I assume is the power supply.  My question after all of that is does anyone have any thoughts on how to eliminate the hum with the Icon Audio preamp? Do you think it is a issue with it being a tube pre. Would a solid state pre have the same problem?
I don’t understand how a extension cord is different than running romax off of a junction box.
The only thing that seemed to help was running an extension cord to the same outlet everything else was plugged into.

hum is as simple as this: Any time you have different paths to ground you risk getting hum.
Your extension cord eliminated the hum because then everything had just the one path to ground.
This one simple rule comes in real handy. Like you would never run multiple dedicated lines you would run one. What you have done is, in a sense, build a system with multiple dedicated lines. Only they aren't dedicated. Just different.
Got it?
So I got the hum to go away. I initially ran the circuit to a junction box and split off to go to each outlet in the separate rooms. I had an extra wire in the run to the living room box. So instead of splitting power at the junction I ran just power through the to the living room box and back to the junction where I picked up ground and neutral on my way to the other room. And the hum is gone.
It sounds like the original outlet that you where using had no ground connected!