For the updated Steam client on SteamOS, there's an auto-detect step on first-boot for SteamOS for setting up audio outputs. Additionally, underscan and overscan and brightness settings have been added to the SteamOS startup UI. SteamOS now also has support for selecting your sound input device within Steam and a fix for device volume not being reset to 100% when changing audio device outputs.
Steam for Linux also has improvements to the error messages and updates to the Steam Runtime libraries.
More details on the latest Steam client changes for all supported platforms can be found at SteamPowered.com.