I have just come across your post below from 2001. I know that this is now twelve years later, but hopefully you'll receive my message!!
My grandmother's maiden name was Josephine Duignan and her line of Duignans traced back to County Offaly. Her grandfather, Peter Joseph Duignan, was there in 1859. His father was a farmer called Michael Duignan and his mother was Mary Kilmurray. Peter had a brother called James (married to Esther Connor) and I believe that there may have been two other brothers: Francis and John. Peter and his brothers all married and had families in Dublin, and each of them worked as a brass finisher.
I noticed that you mention in your post that you are related to Seán Duignan. My grandmother always said that she believed that we were distantly related to Seán Duignan - indeed, there is a slight resemblance between him and some members of my grandmother's family.
I am wondering if you have made any progress in your research, and if you think that there may be any connection with my family?