To be able to hit the F6 button, you must restart the Setup process, and watch the bottom of the screen after pressing Enter on the "Welcome to Setup" screen. There will be some moments of files being loaded, and then you should see a message appear which says "Press F6 if you need to install a 3rd party SCSI or RAID driver". This message will only stay on the screen for a couple of seconds, so press F6 as soon as you see it appear.
After this is done, you will see other messages appear, and it will act as though nothing is happening, but eventually a screen will appear which will allow you to install the drivers for the HBA or controller. The screen will look like the sample below:
After you press S, the driver install process will continue and the floppy diskettes will be needed. Further instructions will be furnished after the driver install process has ended.