| Songs specifically for a 6-string? Well I guess Dream Theater is a good example. But don't get too hung up on them. They are so technical to a point where the music is really missing something. I would suggest Images/Words and Awake if you want to hear some good 6-string bass stuff.
When I play their stuff though, I feel like i'm just practicing. Their is next to no emotion in their music. It's not like playing Rush or something like that who are just far better songwriters on every level.
But as far as lessons, honestly you don't need lessons specifically for a 6 string. You just take what you know on 4 or 5 and expand on it. The point of having more strings, is to actually make things easier to play. You can play more in less horizontal space. Thats really all it is. Just play the 6, be patient and thorough and you'll get good with it. | 
