Should be obvious!
An 1000base-tx port sould only be used with another 1000base-tx port.
it is ment for Cascading two or more OvisLink's and / or use with a Server who has a 1000base-tx compliant NIC.
Cat-6 is usable, but only for short distances.
(No longer than three Metric meters)
Try to obtain some STP cable. (Shielded Twisted Pair)
Be sure to use a Crosscable to cascade two or more OvisLink's.
A Straight thru is used between the Server and one port.