Fellow Irish Rail Travelers,
After waiting several months to purchase advance online discount tickets on Irish Rail, I finally was able to as of August 3.
The customer service folks at Irish Rail first told me that these online tickets wouldn't be available until their Time Tables were set on September 1, then they updated that to say online purchases were available in mid-August.
Since I was bound and determined to get the best seats at the best prices I kept checking back and VOILA!
Hope this helps with your rail travels on the Emerald Isle.
Safe and fun trip to you and yours!