Mickey,
Your best option is a LTV mortgage from NIB.
This would involve transferring your current mortgage to NIB, and getting a much better rate of interest. You could then release equity on this.
If you released €75k, you could use it as a 20% deposit on an investment mortgage for the new property.
You could do this on an interest only basis. It would not be crosscharged.
So for the investment, you would be looking at monthly repayment of €792.66 on a tracker rate of 4.1%