So do you plan to do the first or second method?
Judge by ear... the best way would be to get Sinegen
and play some test tones through your computer, first with the sub off to get a feel for where the satellites fade out, then with the sub on and tuning the crossover frequency until you hear neither a hump nor a null around the crossover frequency.
(cool but very techy stuff follows)
Another cool addition to the PC sound experience would be VAC
routing all system sound to VSTHost
allowing you to equalize all system sounds. This lets you use an advanced parametric equalizer like Electri-Q
to equalize out room modes. The advantage of running Electri-Q on VSTHost rather than on a player like foobar2000 is that you get to equalize the sound coming out of Sinegen too so you can adjust the EQ very effectively.
I run two EQs in series when tuning the EQ on Sinegen
One the draft of the final EQ settings to apply, another a replica of the equal loudness curve of human hearing. This is especially useful to compensate for the steeply decreasing sensitivity of the human ear to deeper bass frequencies while testing (i.e. when playing with Sinegen without equalization you'll hear bass frequencies fading out quickly, it's hard to tell whether this is because of your ear's decreasing sensitivity or because the speakers are really quitting out at those frequencies.)