On top of the advice of @CIJOML i would also advice to use network cables for machines that do have a network outlet. Why? The more machines using wifi, the more chaos no matter what type 2.4 Ghz or 5 GHz you have. In the future it will become even more.
For the machines that can use 5 Ghz, use 5Ghz as it is very durable when having the Omnia in the middle of the office building. Also no interference from 2.4 Ghz waves from neighbors using 2.4 Ghz. If the neighbors are using 5 Ghz, there are still more than enough channels to use to lessen the interference and also 5 Ghz waves don’t go that far so a better alternative instead of the 2.4 Ghz. When placing the Omnia, do place it in the middle, but upstairs. As the waves reach lower places, but more difficult to reach higher places when placed downstairs. Also try to play a bit with the antenna’s.
At home the only machines that are connected to my wifi, is tablet, smartphone and Google Chromecast. All the rest from Raspberry Pi’s to mediabox, to computer to laptop, to NAS are all connected through cable.
About the antenna’s i have with the 5 Ghz antenna’s for example, 1 vertical, one 45 degrees and one 90 degrees (horizontal). The waves will then be send horizontal, vertical and semi-horizontal/vertical.