The number after the first dot is your subwoofer. The last number is overhead / Atmos speakers.
You can add more subwoofers on the Subwoofer step later — layout counts only the LCR, surround, and height positions.
Sets how loudly you plan to listen, and the short-term peak capability your system needs to support it.
You listen around 80 dB. Movie peaks land roughly 15 dB above the average level, so the system needs about 95 dB of peak capability to stay clean.
You listen around 85 dB. Movie peaks land roughly 15 dB above the average level, so the system needs about 100 dB of peak capability to stay clean.
Reference calibration puts dialogue around 85 dB at the seat, with peaks 20 dB above it — so the system needs about 105 dB of peak capability.