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The current image from 2018-03-15 can found here: http://share.loverpi.com/board/libre-computer-project/libre-computer-board-roc-rk3328-cc/image/ubuntu/
It supports common HDMI CEA (consumer electronics association, read: TV stuff with audio support) display modes like 4K, 1080P, 720P, 480P, etc. Some odd resolutions like 1366x768 utilizes DMT (display mode timing, read: monitors and such with no audio). If you want HDMI audio on a 1366x768 TV, you need to set the resolution to a CEA mode like 720P (1280x720) in order for audio to come through on your TV.
Many DMT modes have not been added to the kernel. If you are getting no video but able to ssh into the box, this is most likely the issue. Please let us know and we can add the resolution of your display to the kernel to be integrated into the next image.