Thanks Thom,
I can understand your frustration & yet because your family emigrated, you can go back further than the most of us that never left. Anyway, I wonder was Felix younger, did he get married here? if so you may be able to get the marriage cert & Cavan Genealogy may be able to help there. If he got married here the chances are that he married his next door neighbour as they did not travel far for spouses.
Names also repeated themselves in families, if Patick & Felix were from the previous generation it is chances that their cousins were name likewise, so to find clusters of them, may get us the townland, together with Smith neighbours 1901 & 1911 census at nationalarchives.ie
In my ideal world every one would have their family tree done, last year I amalgamated 3 O'reilly trees through their in-laws, so in-laws are very important, as is gossip, I have discounted some of the stories, only to prove that they belonged to the previous generations, so hold on to all the jig saw pieces, that missing piece may turn up.
I know the McCabes are very active with their clan gathering in Cavan, I could not locate it online, but if you can write to the Editor at The Anglo Celt, they often publish letters looking for family & you will get a larger audience than this site gets at the moment. www.anglocelt.ie
Were there any priests in the family, they are will documented. All Graveyards are not recorded yet & there are some very old ones, this is a big job.
I also trawl www.irishnewsarchive.com ( subscription site) It is very addictive & very sad reading in some cases, however I have seen mention of people getting passages paid to go to america, also if the family had any means there maybe obituaries, which would mention family & where they were, perhaps your families death was mentioned, even in societies, political & sporting as they seemed to always be passing on sympathy at their meetings which were recorded in the anglo celt.
I'm gone all green!!! Dont give up Regards Carmel