[htpc guy]

The intro videos work fine, but when it loads up the OSD bar is present on screen also, which blocks the intro video.
Have tried modified versions of the startup.xml and home.xml for Aeon MQ3 skin without luck

The Aeon MQ3 Startup.xml below

<!-- Aeon MQ 3 -->

<window id="2999">
<onload>PlayMedia(C:\Users\"username"\AppData\Roaming\XBMC\addons\skin.aeonmq.3/introMovie.mov)</onload>
<onload condition="Skin.HasSetting(startplay)">PlayMedia($INFO[Skin.String(startuplocation)])</onload>
<onload condition="Skin.HasSetting(multifunctionwatchlist)">RunScript(script.watchlist,movies=true&amp;episodes=true&amp;albums=true&amp;limit=8)</onload>
<onload condition="Skin.HasSetting(multifunctionrandom)">RunScript(script.randomitems,limit=8&amp;alarm=60)</onload>
<onload condition="system.hasaddon(script.tv.show.next.aired) + !SubString(Skin.String(DisableSubTVShowTVGuide),true)">RunScript(script.tv.show.next.aired,silent=True)</onload>
<onload>ReplaceWindow(Home)</onload>
<onload condition="!SubString(Skin.String(DisableWeather),true) + StringCompare(Weather.Plugin,weather.weatherplus)">SetProperty(WeatherOverride,7day)</onload>
</window>

Anyone able to shed light on additional expressions to fix/hide the OSD while the video plays?

I would suggest asking in the skin thread. Seems that some skins are easier to get working than others and there isn't a universal answer.