The House of Ix is more of a seller and trading house, they deal with many major and minor houses within the imperium including House Corrino, they wouldn't have to engage in war since they make mass profits of of this trade.

Also if you read the Prequal books The House of Ix was in no real state to bolster an army to take over an entire planet. (I know these weren't written when Dune 2 was made but I like to share relevant information)

Zagreus sits inside your head Zagreus lives among the dead Zagreus sees you in your bed and eats you when you're sleeping Zagreus at the end of days Zagreus lies all other ways Zagreus comes when times a maze and all of history is weeping