Hooked up HW-D450 sound bar to Samsung UN40D6000SF TV with low output from sub woofer

Maybe try headphones settings instead of internal speakers and consider the sound bar as headphones. Some TV's may limit output to headphones as well but start there.
Assuming you have a Samsung TV, look at your TV settings.
You may have the sound level on auto.
Next check to see if you are set for the external speakers, you might have to look in additional settings to find this.
Should you have another brand of TV the concept is the same.
so check settings for TV for external output.

Smash away. I don't think you can connect a wireless piece to a sound bar. This may be out of my wheelhouse, but I don't think so.

Try out optical tv to in optical in your sound bar it will work.
Carl

I think your set up is correct. The only other thing you may have to do is to set the sound on your TV to 'External Speaker' (or something similar) from your TV's remote accessing the menu.

It passes infrared signals to the TV (via an IR eye/wand) incase the soundbar covers the TV's IR pickup

easiest way would be to connect the optical audio output from the tv to the optical input on the soundbar. You may have to go into the tv's setup menu and enable the audio output jack

there should be an "auto power" feature that should turn the unit back on once a signal is detected.

don't you mean sound bar to tv?
your tv has an input and output for audio and video,find the audio output and connect the sound bar!

audio output.

If no lights at all come on, then the sub is completely dead and probably needs to be replaced.