This is for people who don't know. For people who do know, please skip this, or add to it. Thanks.
Many Realtek drivers using a digital output require 24-bit Padded when using WASAPI EXCLUSIVE Mode (not WASAPI shared mode or DirectSound Mode). How 24-bit padded differs from 32-bit is: 24-bit padded is a 24-bit digital signal wrapped in a 32-bit package. So, going into your system settings and changing it to 32-bit is different from 24-bit padded (It's not the same).
With my Realtek driver (using digital output), I can use 24-bit integer using WASAPI. However, I must use 24-bit padded if I use WASAPI EXCLUSIVE MODE (Bit-perfect Mode). Amazon Music HD uses WASAPI Exclusive Mode, but it is not Bit perfect, which means 24-bit padded is not needed for digital outputs. Whereas JRiver WASAPI Exclusive Mode is Bit-Perfect. Which then, 24-bit padded is needed for digital outputs.
Also note that In WASAPI Shared Mode, WASAPI Exclusive (non-bit-perfect) mode and Direct Sound Mode, Windows up-convert all audio to 32-bit float and will down-convert if the hardware doesn't support 32-bit. The frequency and bit-depth are converted to what is set in Windows sound settings. So, it would be wise to set the Shared bit-depth and frequency accordingly in Windows sound settings. WASAPI Exclusive (Bit-Perfect) Mode bypasses all of this.