Thanks guys for your replies.
In my scenario, I have two MHOs and two gateways installed in two different racks; rack1 contains MHO1 and GW1; rack2 contains MHO2 and GW2; SYN can be, of course, realized through 2 fiber cables.
Downlinks from GW1 to MHOs could be done in this way?
From MHO1 to GW1 using DAC cable, and from MHO2 to GW1 using fiber (specular configuration for GW2).
All the uplinks from MHOs to internal network could be realized mixing DAC and fiber.
Do you think this could be acceptable?