once you get Roon integration running, roon endpoints are available in Haas as media_player object , which you can control with pause/play, skip buttons in haas gui.
Then, when you integrate Haas with HomeKit (you need to have one apple device hosting HomeKit bridge function - could be ipad/apple tv/homepod/mac), you can then call any automation from HomeKit - thus also with Siri - best thing is that as your apple HomeKit device stays home, you can use Siri on iphone to control devices even when not at home 
As Haas Roon extension is now part of Haas itself, it should be quite straightforward to get it running. If you’d have specific questions i’ll try to answer, but i’m not haas expert 
btw here is live topic on this site related to Roon - Haas integration