Audio device selection on RaspBerry Pi

I’m trying to play audio from a Xojo app on my Raspberry Pi 3 with a 3rd party audio “hat” (Suptronics X400). I can select this audio device on the RPiOS desktop and all applications I run locally play out the X400 perfectly. Xojo apps, however, always play from the HDMI output.

I have tried:

sudo amixer cset numid=3 <n>

This command has no effect on XoJo apps, no matter what the value of n. All Xojo audio comes out the HDMI output.

How can I configure what audio device Xojo apps use?

OS & Kernel info:

PRETTY_NAME="Raspbian GNU/Linux 10 (buster)"
NAME="Raspbian GNU/Linux"
VERSION_ID="10"
VERSION="10 (buster)"
VERSION_CODENAME=buster
ID=raspbian
ID_LIKE=debian
HOME_URL="http://www.raspbian.org/"
SUPPORT_URL="http://www.raspbian.org/RaspbianForums"
BUG_REPORT_URL="http://www.raspbian.org/RaspbianBugs"

Linux pi3-amplifier 5.4.51-v7+ #1333 SMP Mon Aug 10 16:45:19 BST 2020 armv7l GNU/Linux