if you ask me i wouldn't bother with PWM on LPT.
just look up simple DA convertors like in the OLD days.
yes there was time when sound card on pc was unthinkable
or at least VERY expencive. solution in many cases was
simple resistor ladder network connected to LPT to produce
sound in far better quality when compared to PC speaker.
(well it did eat lots of resources to produce audio signal but it worked).
all you need to do is write to the port ONCE when change occurs
(no need for PWM bit banging and hogging pc resources and fighting with
Windows for repeatable timing).
of course analog output will be low, but nothing a simple OpAmp
wouldn't cure.