There's no easy way to convert combat stats from one game system to another. What you have to do instead is replace all the stats with stats from the 5e Monster Manual.
I don't have your XDM book, so let me give you an example using a book I do have. Let's say I want to convert the D&D 4e module "The Slaying Stone", intended for first-level 4e characters, to run for a group of fifth-level adventurers in D&D 5e. (And let's assume that I don't mind the mild incongruity of a group of fifth-level adventurers fighting wolves and goblins.)
Checking an encounter calculator, I see that an appropriate challenge for four 5th-level adventurers is between 1000xp and 3000xp.
The first encounter in the module is against three CR1 "ravenous wolves" and two cr2 "gray wolves". Checking the list of monsters by CR, I see that there's a CR1 monster called "dire wolf", so I replace the 4e ravenous wolves with 5e dire wolves. There are no CR2 wolf monsters, so I'll use something else that looks similar -- perhaps the "dire boar". I copy the dire boar's stat block and change the name at the top to "charging wolf".
Checking an encounter calculator, I see that the battle with five monsters (three CR1, two CR2) gets a 2x encounter multiplier and should be classed as 3000xp, which is too high for the first encounter. I remove one of the CR2 monsters, which makes it a 2100xp encounter which is just right.
So my final encounter is with three dire wolves and one dire boar which I've renamed to "charging wolf".
Later in the module there are weirder monsters, such as Rort the CR2 goblin tomeripper, who casts randomly-selected spells and summons oozes. I'd still call him a goblin tomeripper, but I'd replace his stats with the CR2 lizardman shaman's stats. The lizardman shaman can cast conjure animals to summon reptiles; I'll say that this version of Rort can instead cast conjure animals to summon oozes. (Specifically, four CR 1/2 gray oozes.)