Hi Shahab,
Yes, you can connect an external soundbar via digital optical audio input or HDMI.
You can control your soundbar and subwoofer with the Samsung TV remote by connecting the soundbar via HDMI and Anynet+. With Anynet+, you can control external devices connected to your TV with HDMI using your TV remote. To turn on Anynet+ (HDMI-CEC), go to Settings > General > External Device Manager > Anynet+ (HDMI-CEC).
The outputs available on the TU690T: 2 HDMI ports, 1 USB port, 1 digital optical audio input, 1 ethernet port, 1 RF antenna input, and is both Wi-Fi and Bluetooth enabled.
I hope this helps!
~Samsung Advisor