Sounds like a great 5.1 start. Please do note that the 1723 THX Monitors do not have any type of threaded feet on the bottom of them and the Gaia 2 is a threaded product. What stands were you planning on using? You could look to add the Gaia 2 to the right stand if it supports threaded feet? „Lukas beat me to it above“!
Why not go „FULL SEND!“ on Arendal and shoot for Ambassador status by going with the 1723 2V subwoofer? Double the amount of drivers and the MAYHEM!