You should note that if you daisy chain the boxes in this manner you may encounter some problems with signal pass though as both these boxes have different methods of handling pass through if the box is in standby mode. It relates to the power saving modes. I am aware that the Manhattan has issues with waking up to record a scheduled recording if a particular power mode is selected so the order of the boxes in the chain might be important.
If your quick test works you should also consider using a passive splitter adapter which should be ok if you have a good signal level. This will give independent connection to the aerial signal.
Replies so far have omitted the crucial point of each box needing it own HDMI lead connection to the TV (or AV amp if you use one). That may mean you need to tell the TV which HDMI input it needs to be switched to.