Turns out my BSOD's are all sound related, every single one concerns
portcls.sys.
FH was working fine yesterday (offline), I turn it on today to have a quick round on Totalize against the bots, aaand it blue-screens while 'verifying files' (just before 'Join Game' appears).
PC boots back up, and I repeat the process (same map)...and the exact same thing happens again...
Ok, I think, maybe Totalize is SNAFU in SP, so I try it again with a different map...nope, same fucking problem.
Then I try again with a third, and then a fourth map...all to no avail.
So I set the Sound Quality to 'High', instead of 'Ultra High' and I finally succeed in loading a map...
I'm going to reinstall the drivers later to see if that makes any difference.