To the OP:
Unfortunately, you are finding yourself in the same position that anyone who wants to start working with HDR in any meaningful finds themself in. In order to work with an HDR workflow, you will have to buy a Decklink card or the equivalent. You will also need a monitor which is a true 10 bit panel with HDR capabilities, or perhaps a TV like an LG CX. As a previous poster mentioned, the 400 nits your current monitor has, just won't really cut it. Unfortunately, at present, HDR is an expensive proposition, but the tradeoff is that it is nothing short of an amazing, intoxicating experience to work with and you won't regret spending the money to make it hapoen. I know I didn't.