speakers and cables

Too bad @erik_squires has left the forum. This is an area where he could answer in his sleep.

I believe the correct way to wire it is not in parallel but in series.

Take the left speaker wire to the left input of your sub "speaker level input’ and then go from "speaker level output" to your speaker. same on the right.

Do not hook anything to the right speaker on the left sub and vice versa.

And I don't think you need a high pass filter, The sub has all it needs between the speaker level input and output.

Jerry

I would stay away from y splitters.  Y splitters hook 2 sets of drivers in parallel, which halves the inductance.  So the amp current doubles going into the low impedene load and it  trips.  You are lucky your amp has a breaker and does't just fail from the high current.

Never hook 2 loads up in parallel to one set of speaker outputs.

Jerry

Sorry I didn't follow everything going on here.  Y splitters on the RCA low level signal are ok.