If it's Convolver 0.3 then it's what I'm using. Works with my foobar 1.1.1, but no idea if newer versions support it.
More important, though, than the software, is the impulse response you feed in. Meaning, you'll want to start with getting an electret capsule microphone for a few bucks and attaching it to some sort of a round disc so you can get a seal on the phones. Then measure the channel balance. (Yes, I've experimented with this - you don't need an accurate response measurement to fix the channel balance, you're only interested in the relative difference between the channels. As long as you measure them identically, you ought to be fine without a fancy calibrated microphone.)
I have a few reasonably decent mics left over from recording days. I will have to dig them out of the archives (no easy feet when you have an electronics graveyard like mine:)). I was thinking of using a silicone pot holder with the centre cut out to seal the mic to the headphone.
I have a fairly good source of test tones and sliding scales, but am curious as to what you are using for the actual measurement.