In general, it is a good idea for speakers to 'match' in the sense of similar timbre or pitch response.
So, while technically it should be possible to run 8ohm speakers as fronts / center you may find yourself being able to point at them instead of simply disappearing as perhaps they should. Depending on your tolerance to this, you may be able to get away with a less than perfect match.
Also, Gregm's comment about sensitivity are well found. Doesn't appear you have much power here, so make the most of what you got!
Christmas is coming and 'upgrade fever' can strike at any time.