I have put this summary in the Key Post.
Is it correct and comprehensive?
The maximum either spouse can contribute is a percentage of their salary. This percentage is determined by their age.
It is better to max the contribution for the lower paid spouse especially if there is any danger that the higher paid spouse's fund is approaching the €800k limit on which 25% can be taken tax-free.
Of course, where either spouse has an employer who matches their contributions, that spouse should contribute the maximum which the employer will match. This takes precedence over all other considerations.
The first €33k of her income is taxed at 20% irrespective of his earnings.
So her pension contributions should not bring her income below €33k.
It is better for him to make the contributions and get 40% tax relief.
For example, if she is earning €40k, she should not contribute more than €7k to a pension.