If I were to recommend a cornerstone for a canon of chamber music for double bass and guitar I would personally insist you have to start with the works of Annette Kruisbrink.
Cirex is a duet that shares a number of gestures in common with a work called 60+
That piece is fun and is one of the better examples I can think of of post-minimalist guitar music.
Cirex, however, I feel is sublime. :) Adding that double bass part takes the ideas to a new and more glorious level!
I'd blog at significantly more length about this because I most certainly have the score and have been wanting to write about this work for years but I have a lot of music I'm trying to write about ... and I'm trying to write about it in the way that I write about it.
So a more detailed score discussion can happen later. For now, I hope you enjoy Cirex.