Powered Sub Crossover

I am trying to add an old yamaha powered sub (like a YSTFSW050BL but much older and has no crossover as it relies on the amp) to my simple AV system (I have a TV where all inputs go to and I use the ARC channel to a Samsung sound bar). My Sound bar doesn't have a sub output so I have taken the optical out from the TV and pushed it though a small gizmo to turn this into a Left and Right analogue signal, one of which I tried plugging into the back of the sub. It works but it sounds awful, which I assume is because it's getting frequency range that it shouldn't be.

So I tried ordering one of these (NE5532 Low Pass Filter Board Subwoofer Volume Control Board Amplifier Module 9-15V Module Board from Electronic Components & Supplies on banggood.com) but I get nothing out of the module. So either the module is a dud, or I am barking up the wrong tree and I need to find a different solution.

Any ideas if this should work? Or should I look at something like a speaker crossover? (will this work with line level signals?)

Thanks.
 
One thing I CAN tell you to beware of optical to analog converters that are stereo only. When presented with
5.1 they will make some really bad screeching. The 5.1 converter will do proper stereo if presented with
stereo only. To get the sub you either need to mono mix the L and R but in 5.1 those might be limited to
80 Hz. In 5.1 mode the sub gets its own feed independent of L and R. A stereo only feed will be full
bandwidth L and R so you need to mono mix and filter at 80 Hz.

I did what you want and more in this.
5.1 channel preamp

 
Interesting project, but a little beyond me.

The gizmo is stereo, but no screeching. I need to delve deeper.

The real reason I am trying to use the old sub was to prove that the "concept" of taking the optical though the gizmo to the sub would work and then I was going to invest in a newer powered sub with stereo inputs and frequency adjustment built in.
 
So I tried ordering one of these (NE5532 Low Pass Filter Board Subwoofer Volume Control Board Amplifier Module 9-15V Module Board from Electronic Components & Supplies on banggood.com) but I get nothing out of the module. So either the module is a dud, or I am barking up the wrong tree and I need to find a different solution.

Is that 9 to 15 volts AC or DC voltage? I've seen both.
 
I can't find any suitable power supply off the shelf, and not sure my electronics skills extend far enough to build one.

Will a passive crossover like usually find inside a speaker work with a line level signal (I could probably build one of these) or do they need an amplified signal?