You will need a separate connection for sound, yes. How to achieve this will depend on what outputs your laptop has - if you have a standard 3.5mm output (looks the same as a headphone output), then you should be able to connect this into your TV with a 3.5mm cable (the input on the TV will look the same and will be close to the VGA input). Otherwise, you could possibly connect into your Nait5i-2 with a 3.5mm to RCA phono lead.
If you have a DAC and if your laptop has an optical output, you could connect via this into the DAC. Remember, you'll probably need to configure Windows (or whatever your operating system is) to output via this connection.
If you have none of these options, you'd need to look into getting some kind of USB sound card which would give you one of these connections.