There's no need to run two RCA sub outs to the SMS-1, since the sub output is mono anyway. I'd run a single cable from the AVM30 to the SMS-1. The SMS-1 does pass signals between the XLR and RCA connections, so you can connect the AVM30's balanced sub out to the SMS-1 and then send an unbalanced signal to a sub. XLR and RCA outs aren't an exceptionally appealing option, but I have seen some XLR splitters.

I'd recommend disabling the SMS-1's crossover and letting the Anthem handle it - having two crossovers in series at the same point is going to get you to a weird place when you consider the two crossover slopes. If you move the cursor to select the low pass crossover setting for the “Setup” preset (in the System Settings menu), press “SELECT” to edit the crossover, and then press “RESET,” the SMS-1 will turn the low pass crossover off.