Bummer about no-speaker access for extensions. That seems an oversight but perhaps the version of Android under the hood prevents it.
Here’a a couple of video shorts regarding Xert Magic Buckets on a Karoo 3 –
Install EBC: https://www.youtube.com/shorts/BxOCFne5SMs?feature=share
XMB Tips: https://www.youtube.com/shorts/5ZUfouEpBW8?feature=share