Hello-
I'm not quite sure that I'm following exactly what you need, but I have an idea. You would still use pricelists to complete this action. One thing you'll have to keep in mind is that pricelists look/act different depending on the version you're using. It looks like the screenshots above are from v12, and I use v11.
What I would try, is going to the price lists (in v11: sales > pricelists). I believe your discounts are applied to anyone purchasing large quantities, so I would open the "public pricelist," edit it, and add a line. When you're adding a line, you're able to select that you want to add product variants.
The above route would allow you to discount single variants (ex: purchasing product A variant A for $10, but discounted to $8 if purchasing more than 10 of them). If you also want to discount across multiple different variants, you could create another rule within the same pricelist for the product (instead of the product variant). In this case, you could say 10% discount for any variant of product A if purchasing more than 10 total.
Hopefully this helps!