Dfplayer pro hasn't line out - help build one!

Dfplayer mini has two ways to output audio:speaker and stereo line out
Dfplayer pro has only dual speaker out without common ground.

I 'd like to connect Dfplayer pro with external amplified speakers so I must have something like line out with common ground.
 I found one or two ways to make a common ground output but neither worked. 

Firstly I tried a capacitor (100uf) at positive output. Secondly I tried capacitor and resistor on negative output. Nothing worked. I have sound but with extreme distortion - maybe dc current or very high voltage output.

Any ideas to have line out?