If you listen carefully to the solos, you can pick who is playing them, because all three have very distinctve styles and sounds. Ok, in some of the harmonised licks where both are playing at the same time, it can be difficult, but for solos, generally -
Dave uses his neck pickup a lot, and has excellent legato (=finger speed and accuracy) which gives a very distinctive smooth sound, with minimal pick noise.
Adrian has a more varied tone, with different timings, and uses the pick a lot more.
Janick's solo's tend to have blisteringly fast licks in them, which can get a little confusing and muddy, particularly on the live stuff.
Also, on the LAD DVD, Dave is in your left speaker and Adrian in your right. Solo's are usually centred. Listen and you'll work it out.
With Death on the Road DVD's, Dave is Left, Adrian is Centre (can be quite hard to hear when he's not soloing), Janick is Right. Solo's are usually centred (All assuming that the CD is mixed like my stereo DVD).
Stick on some good headphones and I'm sure you'll work it out, but I could have a listen and write it down for you.