Do not at all agree that the OP must move to DC. It looks like a company takeover and there are rules on this, so that it's a transfer of undertaking and the OP should be still employed as though it was a seemless transfer.
Next question then is what are his rights. Can companies just change the pension scheme, or do the employees have to sign something. So the OP needs to get professional advice from an expert in this area.
This happened to my husband a few years ago, big push for the DC, naturally as it costs a lot less than the DB. Documentation to bamboozle you, but would convince you DC was the way to go. Needless to say he stayed with the DB. It was a large American group, also based in Ireland, but this happened elsewhere in Europe and I'm sure the OP must have the same rights as my husband did. He should not be bullied just because they are a big company. And he most certainly should not sign anything until he has his facts straight.
He should also be aware that pressure can be brought to bare elsewhere, signing away your rights with a new contract, or threat of redundancy etc.