Train from Belfast to Galway

I want to take the train from Belfast to Galway and can see the options when I go to Irish rail, but since the trip originates in Northern Ireland, I can't book the trip on the Irish Rail site. They tell me to go to the Translink website. Once there, I can't figure out how to actually buy a ticket to Dublin. They show an itinerary, which involves taking the train to Connolly train station, then walking to a local tram, taking the tram, then walking again to get to Heuston station. Seems like a lot of extra hassle, but I'm willing, but then I can't figure out where on the site to actually book there tickets? Anyone else experience this? Is there another way to book the whole journey ?