Wildgoose,
While your situation is very close to the traditional understanding of a marriage, AFAIK the union you have chosen (PACS) is a type of civil partnership, and not a civil marriage. Dreamerb rightly points out that friends and same-sex couples etc can sign up for this, which means that this form of union is not officially recognized in Ireland.
The easiest way to find out is to call the Revenue office for your area to confirm.
Please let us know how you get on.
JR