Using different subwoofer with sound bar, possible?

[ttamez]

Here's my dilemma: I upgraded my main sub in the living room so I decided I wanted to use my old polk 12" in the bedroom, where i have the polk surroundbar 6000. The problem is the 8" subwoofer it comes with is wireless. What I currently tried is using the RCA audio out on the TV to the RCA in on the sub, then the RCA out on the sub to the soundbar's 3.5mm (I was previously using optical audio out on TV to optical in on soundbar). This works, but the problem is when I adjust the soundbar volume, the subwoofer does not change volume. The TV volume does not control it either. The only way I can adjust the subwoofer volume is by changing the gain on it, but that's not really even the same. This would be no problem if the soundbar had an audio out, but it does not. I thought of the possibility of adding a cheap receiver to the mix, but then I will not be able to adjust my soundbar volume (at least not with the receiver, right?). does anyone have any ideas on how i could make this work so i can adjust the soundbar volume and it will adjust the subwoofer accordingly? or is this just not possible, since the soundbar packs the whole "system" inside it and I cannot power the speakers externally?