Have people listened to the playlists that the author made? I've listened to those playlists and they seem to fit as well. Just an idea tho. I think the song "The Truth" by Kygo & Valerie Broussard is a great song that seems to fit the novels.
The two songs that immediately leap out to me moreso remind me of certain characters rather than the series as a whole. Sleepwalk by Forrest Day reminds me of Clancy (specifically his dynamic with those he knows) and Get In Line by Barenaked Ladies extrudes such an immense Chubs energy it hurts.