For "Or" to work, you need to wrap in parenthesis...
Try:
([Album Artist]=[Abigail Washburn],[Bap Kennedy],[Belinda Carlisle],[Bert Jansch],[Billy Joe Shaver],[Bobbie Gentry],[Bonnie /"Prince/" Billy],[Brandi Carlile],[Chip Taylor],[Chip Taylor & Carrie Rodriguez],[Dar Williams],[Dave Alvin],[David Olney],[Eleanor Mcevoy],[Greg Brown],[Grey DeLisle],[Guy Clark],[Holly Williams],[Iris Dement],[Jimmy Webb],[John Hiatt],[John Prine],[Jonatha Brooke],[Emmylou Harris],[Gretchen Wilson],[Kate McGarrigle],[Martha Wainwright],[Mary Gauthier],[Mary Coughlan],[Sally Timms] or [Composer]=[Abigail Washburn],[Bap Kennedy],[Belinda Carlisle],[Bert Jansch],[Billy Joe Shaver],[Bobbie Gentry],[Bonnie /"Prince/" Billy],[Brandi Carlile],[Chip Taylor],[Chip Taylor & Carrie Rodriguez],[Dar Williams],[Dave Alvin],[David Olney],[Eleanor Mcevoy],[Greg Brown],[Grey DeLisle],[Guy Clark],[Holly Williams],[Iris Dement],[Jimmy Webb],[John Hiatt],[John Prine],[Jonatha Brooke],[Emmylou Harris],[Gretchen Wilson],[Kate McGarrigle],[Martha Wainwright],[Mary Gauthier],[Mary Coughlan],[Sally Timms]) ~sort=[Name],[Artist],[Album Artist],[Album],[Album Artist (auto)],[Disc #],[Track #]
Does that work any better?