So for some reason I can't edit my post anymore. I want to share my final configuration:
args: -netdev type=tap,id=net0,ifname=tap100i0 -device e1000e,mac=E6:66:08:41:7B:E4,netdev=net0,bus=pci.0,addr=0x12,id=net0,bootindex=300 -netdev type=tap,id=net1,ifname=tap100i1 -device e1000e,mac=E6:66:08:41:7B:E5,netdev=net1,bus=pci.0,addr=0x13,id=net1,bootindex=301
balloon: 0
boot: cdn
bootdisk: sata0
cores: 4
ide2: none,media=cdrom
memory: 6144
name: XpenologyDSM
numa: 0
ostype: l26
sata0: local-lvm:vm-100-disk-1,size=52M
sata1: /dev/disk/by-id/ata-WDC_WD30EFRX-68EUZN0_WD-WCC4N5HPLJXC,size=2930266584K
sata2: /dev/disk/by-id/ata-WDC_WD30EFRX-68EUZN0_WD-WCC4N0853082,size=2930266584K
scsihw: virtio-scsi-pci
serial0: socket
smbios1: uuid=e5f1edb1-dbaf-4566-ab3e-5fb8e09c9ed7
sockets: 1
unused0: local-lvm:vm-100-disk-0
vmgenid: 7d73c95b-8881-4b29-8148-ce5ba7ce3df2