Another thing you might consider doing is firewalling in the server to refuse connections to 192.168.1.0 for filesharing ports. This will immediately "break" whoever is using that address for filesharing and then you can go fix that so all your fileshare traffic is on the 10.0.0.0 subnet and stays in the switches, where it can max out the switching bandwidth without a big reserve in your router QoS.
If the 3 operations, sales, and warehouse switches are currently gigabit dumb switches, changing them in-place to 24 port Zyxel smart switches at $100/ea would let you configure QoS in those switches for DSCP tagged phone traffic. Once you rewire and have your nice modern set up, you'll be able to reuse those smart switches anyway, so they are a good investment in improved VOIP traffic. If you do this, the dumb switches could still be used to handle the phones for example. Just put an uplink between the dumb switch with all the phones hanging off, and the smart switch. Then tell the Zyxel to retag DSCP on all the inbound traffic to that port where the dumb switch is plugged, so all the phone traffic gets high prio DSCP tags, and goes through priority queues before any filesharing traffic.