One of the Optical is losing sound once in awhile for 1 second
I assume this has been checked by swapping cable and devices to make sure it is the receiver and not the cable or source device.
I wouldn't try to combine two signals. As 57 says it won't work with some devices and could cause unpredictable results with any devices.
As 57 said, a 'Optical to Coaxial Digital Audio Converter' may be what you want. There are some on Amazon.ca for $15-$30, including shipping. If possible, I would buy a well known brand such as Cables-To-Go or Monoprice.
A remote controlled 'Optical Digital Audio Switch' would also do the job. Several are available in the same price range.