TMC2208 / A4988 - which goes where?

I'm on Stage 08 → Steps 19 and 20, and I'm installing the stepper drivers. I have:

• 3 x white TMC2208 stepper drivers

• 4 x red A4988 stepper drivers

I ordered the following upgrades:

• Heated bed

• Flexplate

• Power pack

• Dual extrusion

• Silent printing upgrade (3 x pieces)

I'm confused as to where I need to install which stepper drivers. I have 5 holes on the control board (as far as I can tell) in which stepper drivers can go. I have 2 of the white TMC2208 boards in the left-most holes (identically to how the guide suggests).

Should I leave the other holes empty? Or should I install some stepper drivers in them? If so, which ones: white or red?

Below: A picture of what I have installed already. Note the extra 3 holes to the right of the white TMC2208 boards. I now have 1 x white TMC 2208 + 4 x red A4988 boards left.