The Ardhowen Theatre arts centre in Enniskillen often has music events - I just missed Arty McGlyn & Nollaig Casey when I was over there a couple of weeks ago

28th June (too late for you!) has Padraig Rynne, Tola Custy & Paul McSherry

The Clinton centre also has occasional music events

Sessions listed in About.com -
Enniskillen - "Blakes of the Hollow" - Friday or Saturday
Enniskillen - "Bush" - Monday
Enniskillen - "Railway Hotel" - Sunday
Enniskillen - "Vintage" - Friday

Can't speak for any of the pub sessions, but Fermanagh has quite a few traditional musicians, so possibilities should be good. Have a good trip.

Ross