I've got Sky SD with the suitable blue access card, but want a better STB with HDMI without paying for MySky.  It would be nice to also play AVIs.  What should I look for in an STB to know if it will work with Sky?  I'm specifically considering http://airbox.tv/media/djcatalog/Airbox%20S505.pdf which is a clone/rebranded/OEM of Medi@Link Black Panther.  I will likely look further so keen to know what are the specs to look for.  Thanks.