If you're not talking about adding other computers or software to the mix then, yes, IPsec or the built-in VPN functioinality in Windows is the only built-in way to encrypt CIFS/SMB traffic between a Windows Server computer and a client.
You could, obviously, stick hardware-based encryption devices between the client and the server (VPN gateways, routers doing IPsec tunnels, etc). You could install third-party VPN software onto the client and/or server, as well. You can do anything you want to encapsulate, encrypt, or otherwise slice-and-dice the packets once they're on the wire, as long as by the time they make it to the server computer they're decapsulated, decrypted, and glued back together.