For some reason the HDMI audio option is missing from the phonon list on KDE 4.10.x on my HP DV7 laptop. I can't get any audio to output over HDMI. Video plays fine. When connected up to my Raspberry Pi it outputs audio and video just fine.

What video card do you have on your laptop? Some drivers (e.g. the radeon driver) disable HDMI audio by default.

On my system at least, which uses Pulseaudio, HDMI is offered as a seperate audio profile.

The active audio profile can be selected at System Settings > Multimedia > Phonon > Audio Hardware Setup. This is simply a visual interface to configure Pulseaudio - KDE has no control over how the audio itself is actually handled here.