KMS enabled, no HDMI audio

[triffidl]

Pi Model or other hardware: 4B
Power Supply used: 5V 15W
RetroPie Version Used: 4.7.19
Built From: SD image
USB Devices connected: None
Controller used: Bluetooth Xbox One
Guide used: https://forums.raspberrypi.com/viewtopic.php?f=29&t=269769&p=1636828#p1636828

Following the above guide, I've updated my config to use the full kms, and made the following changes to my config.txt:

disable_overscan=1
# dtparam=audio=on (commented out)
dtoverlay=vc4-kms-v3d

I also replaced the alsa card vc4-hdmi config with the one provided in the guide. Sound has not been restored, and there are a few problems. I couldn't find a forum post with quite the issue I'm experiencing, apologies if this is a repost.

alsamixer lists vc4-hdmi-0, but shows the error This sound device does not have any controls. Attempting to run amixer produces no output at all, regardless of parameters. I presume there is an error, not sure where to look for logs. The audio setup warns On-board audio disabled or not present. I understand this is to be expected. I'm also seeing Unable to open SDL mixer ALSA: Couldn't find any hardware audio formats.

Alsa configuration seems to be at fault here- any advice on how to resolve appreciated.
EDIT Have done some more reading and the KMS have a lot of known issues. Was trying them to address screen tearing. I've reverted. Disregard post, apologies all.