If the headunit has a sub out then you will need a mono amp to drive the passive sub. Power specs on HTS systems are very inaccurate so your choice of amp will be a bit difficult. Sometimes the woofer in the cabinet will be marked with the impedance/power or a make and model number you can check out.
If not then you will need a crossover/amp to connect to your headunit. If that doesn't have line level outputs you will also need a speaker to line level converter.
As a last resort regarding the above, as high-level connections aren't the best, many single-channel amps do have high-level inputs, which sum to mono for a single sub. You must connect them either where the main (L/R) speakers are connected to the head unit or amp, or remove the main speakers themselves, connect to them and run wires to the amp.
Here's an amp with high-level inputs, as an example. Check the impedance of your Samsung sub, in order to know what power level of amp you need for decent SPL. The lower the impedance, the more power the amp will deliver.