Things such as sound absorbing and diffusion panels are typically used for improving the sound quality of your room after it has already been soundproofed. They will do nothing to soundproof the room.
The problem with any kind of sound proofing or room within a room method is that it is very expensive. 15 years a ago, I knew a guy who soundproofed his garage so he could play his drums and the materials alone cost him $5000. It wasn't even completely soundproof either because you could still hear the drums if you got within several feet of the garage.
Your subwoofers will be especially difficult to soundproof especially in an apartment.
The only suggestion I can think of is to move to a town where houses are more affordable. I hope things work out for you one way or another.
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