If your XigmaNAS server is a bit slow, it's often beneficial to see what is your network speed before changing settings - especially if you are on wireless. If your network cannot handle more than 50 Mbps, you cannot complain when you have only 5 MB/s Samba transfer rate.
While there are many ways you can check the speed, I usually find iperf3 the best choice. Not only it comes preinstalled on XigmaNAS, but you can also download precompiled binaries for Windows, Linux, and BSD to start with. If that's not enough, you can always use freely available source and compile it yourself.
My approach is first starting server on XigmaNAS (or FreeNAS if that's your NAS platform of choice):
Terminaliperf3 -s
Once server is listening I run the following commands on client, giving it IP address of that server:
Terminaliperf3 -c 192.168.0.1
And that's it. This command will send data for 10 seconds toward server and receive back the same from it.
Armed with the number you can now deal with that pesky SMB3 performance.