I haven't read all the posts in this thread in detail, sorry, but I saw that melodeonboy put "In which case you could try Quimper/Kemper. Much smaller than Lorient and with a higher proportion of Breton music. And the town's beautiful! "

May I add, it would be worth considering the time you are going within those months you mentioned...we stayed just south of Quimper, at Plobannalec for the last two weeks of August. When we stayed there in previous holidays at the beginning of August, we went to a few different music events but this time we couldn't find anything on at all which was disappointing. I meant to put a thread, asking, on here before I went and didn't get round to it, so it probably serves us right! I think certain times of year are much better than others, like in Britain.
We went to a wonderful music festival and parade one year, up near Pointe de Raz (please excuse spelling, too idle to check map, tonight!)
It is a beautiful area, though. Give me a shout nearer the time if you go there and want info on some of the places.