Xiaomi Gateway connect Hue's and Lightify's?

I have already 3 Gateways (Xiaomi, Philips, Osram) already and thats really too much.

My favor is the Xiaomi Gateway because the features of it but how can I connect to Philips Hue Bulbs or Osram Lightify Switch or anything else connected to Xiaomi? All of them are using Zigbee and should be possible. Did somebody do that?

Not necessarily. Zigbee is not as strict of a standard as others like Zwave. Two Zigbee products are not guaranteed to be compatible with each other.

I did a quick google search and I’m afraid I still don’t know if it is possible.

i dont think its possible to link all of them with xiaomi gateway.
but it should somehow be possible to use a zigbee usb stick on the server and connect them all to it?!