For anyone curious, I was trying to migrate a Windows VM from QNAP to Proxmox, and this came in handy. Notes...
- The VM type can be set to Q35/UEFI.
- There may be multiple disk images on the QNAP box for the same VM: you need all of them in the same directory for the QCOW tooling to work correctly. Turn off the VM in Virtualization Manager, and copy them over to Proxmox via SSH; you can also download them via File Manager first.
- importdisk on the latest file; it'll rebuild a RAW file where Proxmox keeps the data.
- Mount the file in Proxmox as an IDE drive, and don't forget to set the boot order ahead of CD-ROM & Network.
- https://github.com/virtio-win/virtio-win-pkg-scripts has the latest guest drivers for QEMU/KVM. https://superuser.com/questions/1057959/windows-10-in-kvm-change-boot-disk-to-virtio has some strategies for migrating from IDE to VirtIO; again, don't forget to check the boot order when detaching/re-attaching the disk image. Adding a tiny VirtIO drive while the system was up, shutting down, detaching the two drives & attaching the main as VirtIO; was the working solution for me.
- Side note: unless you remember to look up your virtual MAC address in the QNAP VM, you'll need to reconfigure your network adapter after migration.