Actually the above sentence is irrelevant. What matters is subwoofers use large speakers that use large drivers (magnets) and magnets can have a very adverse affect on RF (radio frequency) signals. I can think of no worse place to put your wifi antenna than on top of a subwoofer.
The subwoofer needs to go on the floor and the antenna up high (even mounted on wall is good). You don't have room for both the PC and the subwoofer on the floor, so as FE recommends, put the sub on the floor and the tower on your desk. But do NOT put the antenna on top of the tower. The next worse place to put a wifi antenna is next to (or on top of) a big metal object.