Media Center is supposed to be writing iTunNORM tags to the files during conversion, which should work with SoundCheck.
I don't have an old iPod to test this with though, and for some unknown reason, there's no other way to get Media Center to write these tags.
If you are enabling DSP for this during conversion, it will actually change the files rather than performing the volume adjustment via DSP as SoundCheck would.
And you cannot combine Volume Leveling with Adaptive Volume during conversion.
Adaptive Volume in the peak level normalization mode will only work when Media Center knows the playlist.
You would have to enable Volume Leveling on its own if you're performing a conversion.
Adaptive Volume on its own would make the tracks as loud as possible, but would not keep the level even between tracks.
Unfortunately, with high impedance headphones and an iPod, if you were to just enable Volume Leveling on its own - which should produce a very even level of volume across tracks - it's almost certainly going to be too quiet; especially if you are already finding the volume too low.
I think you might have to look into buying a portable amplifier for your headphones.