Only a few inches .... wuhahahaha! Here is my crazy plan!
Build 3 Tower 2Pis.
Lay a Tower 2Pi sideways underneath the screen (put the tweeter on the right of the woofer when standing up). So, you have a Tower laying sideways under the screen with the woofer and tweet aligned vertically with the center of the screen.
The sideways tower covers more to the right than to the left but you could put components in the space on the left. Its tweeter is above the woofer with the same spacing as a regular tower. If the tweeter needs more baffle around it, put a little arch around the tweet. Tip the speaker back a bit so the tweet is pointing at the head of the center seat. Angle in the side speakers so they point at the head of the center seat (Wayne prefers to cross them in front of the center)
Now you have 3 'matching' front channels. Set your amp so the L C R are 'large' and you'll have serious bass. The center will be getting its proper bass which I think is extremely important. Now you can move your other subs around the room to smooth the bass.