The Cree bulbs are zigbee, not WiFi. Strengthening the Wi-Fi might make it harder to reach the devices because WiFi can drown out zigbee. It definitely won’t make anything better.
So the first thing I would do if you don’t need it for any other reason is just to unplug that new Wi-Fi system. It can only make connecting to the Cree bulbs worse.
Second, Garages are always awful. Lots of concrete, lots of big metal boxes (cars, often washers, freezers, etc). Frequently extra insulation in the walls. Just a pain. So the next thing I would do is put one of the Cree bulbs in the kitchen or someplace and see if it connects there. If it does, you know the problem is likely the local architecture. At that point we can talk about ways that you might address architectural issues in the garage.
Third, you might go ahead and take a look at the how to article in the community – created wiki on automating an out building. It might give you some more ideas. But definitely look at the first two things first.
http://thingsthataresmart.wiki/index.php?title=How_to_Automate_an_Outbuilding
( Also, no one but me cares about this, so you can go ahead and laugh now, but for technical reasons it’s a Hue bridge, not a Hue hub. Which is why it says “bridge” on the box. I’ll be quiet about that now. 
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