Well, let’s jump straight in the cold water here: in the corner. A subwoofer is a spheric sound source, meaning it really radiates sound. You can imagine it like something that radiates big water waves. If you imagine that, you can already see some problems coming up in the room, because water waves will be reflected. That’s what happens with the subwoofer. If you move it out somewhere in the room, no matter where; everywhere you will get a delayed reflection from the wall behind it You also get a delayed reflection from the side wall. Having 2 subwoofers, you get it 4 times. That makes things really complicated. Some sound waves collide with each other, they build up and cancel out each other. You end up with a very uneven bass response.
There is one spot in the room where things are much more defined and that is in the corner. In the corner, the bass wave from the actual woofer, the reflection from the floor, the wall behind and beside is almost the same. So it’s really on bass punch, one impact, one kick but without these delays and delayed reflections. That’s what is really good. But it’s too loud. You gain some dB of bass with every corner and the floor. But that will be corrected in the speaker calibration anyway. The punch is better, the timing is better, the dynamics are better. You gain a lot and being too loud will be covered anyway. The corner is really the best spot, in collaboration with correction though.