Digests are integrated with normal ezmlm lists if you use ezmlm-idx>=0.30. Just add the ezmlm-make(1) -d switch to your list setup. To add digests to an existing list created with ezmlm-idx>=0.23 use:
% ezmlm-make -+d DIR
For ezmlm-0.53 or older lists, you just need to re-specify also other switches and the other ezmlm-make(1) arguments.