Mac user here.

At first P8 would open with the automatic settings window and I only use the manual ones, but now I just made a test.

I opened P8, went to Render settings, changed to manual settings and chose "Save settings".

Then to Poser Preferences, Documents tab, clicked "Set preferred State" (Launch to preferred state is selected), clicked OK and closed Poser.

When I restarted: Bingo! the manual settings window comes up.