Both fine, and especially the Breathnach one was a great introduction but they are of their time and perhaps a bit dated at this point. The state of Irish music has drastically changed since and insights in history and development have evolved quite a bit since.What about these two
Maybe Gearóid Ó hAlmmhurain's Flowing Tides : history & memory in an Irish soundscape should get a(nother) mention in this context, as at least a recent work. If you can digest the thundering academic prose.
For the photographically inclined Jim Maginn's The Light of other days, Tony Kearns' Music and Light, Con Kelleher's Arís! and the Blooming Meadows (with Nutan's photos illustrating the interviews with musicians) should be on the reading list. As well as work by Alen MacWeeney, Christy McNamara and Jill Freedman.