If you get a long distance (AVE) train ticket from Madrid to Seville, it comes with a free local train ticket anyway (ie airport train station to the main train station atocha/chamartin), so I don't think the cost is relevant?

What's the price of the DUB-MAD + Train vs bought all through IB? Bought through IB comes with delay protection (both directions), ie a true connection, so that's great, but at what premium (if any)?