Try Railworks America - you will find a number of sounds mods on that site http://railworksamerica.com/
They need the Amtrak P42 DC 'Empire Builder' Loco Add-On, but I only have a p42DC on the Miami West Palm Beach route.
Here you go: Updates sounds, physics, and textures https://www.trainsimcommunity.com/m.../i2385-amtrak-p42dc-empire-builder-super-pack
Surprised no one has mentioned the TruRail Simulations P42DC Enhancement Pack. Their website was down for a couple months but they offer the best version in train sim in my opinion. https://trurailsimulations.wixsite.com/mysite/ge-p42dc-ep