Sub wiring help, high level speaker terminal to RCA line level Sub inputs

I just received a new Rhythmic L12 sub, and surprisingly did not realize it only has RCA line level inputs. I had purchased it thinking it also had high level speaker inputs to connect it directly to the speaker posts on my power amp.

I have a Cambridge CXNv2 connected to a Schiit Aegir Power Amp through the line level RCA. Now, the CXN does have an additional balanced XLR out, but I can only connect the Schiit Aegir through RCA.

So these are my options and questions:
1. Connect the Power Amp to the Sub using a custom cable with speaker terminals on one end and RCA on the other end.
2. CXN XLR --> Power Amp RCA, and CXN RCA --> Sub RCA
3. CXN RCA --> Power Amp RCA, and CXN XLR --> Sub RCA
4. Return the Rhythmic and get an SVS SB1000 with high level speaker inputs.

In this case I’m not sure what the positives and negatives are about trying to connect the Sub via speaker terminals or RCA line level on the CXN. Or is it even advisable to use a cable that goes from the speaker terminals to the RCA line level inputs of the Sub?

Appreciate any help!