Still working on this.
Need to alias the bond “ip link add link bon0 name bond0-alias address 11:22:33:44:55:66 type macvlan” doesn’t quite work because the bonding driver just flips through the same slave interfaces regardless of whether alias or original bond0 device is being used.
Next thing to try: alias the slaves and create a separate bond from them. This is on the NAS box (CentOS 7) running NFS and Samba.
On the Windows side, Server 2016 is running on Proxmox which is using a similar quad-NIC LACP bond. A duplicate virtIO interface was added to the Windows guest in Proxmox. Windows guest seems to be sending and receiving over both interfaces quite happily (but only at half rate), not sure what Proxmox/Linux is doing on the host side yet.