On the sub you can either use a Y split RCA cable or simply go to one channel. If you're using a single, non-split cable, I think most go on the right, but I don't think it really matters. You really don't need a Y split cable though, since the HK only has one channel out. Subs that typically have the right/left in also have right/left out, meaning the sub is doing the crossover work for the rest of your (2 channel) speakers. The AVR 1700 is now doing the crossover work, so you don't even really have to mess with the crossover on most subs unless you want to bypass the reciever's crossover processing.
On the subwoofer turn the X-over filter to the highest frequency...
If not, one has (2) X-overs in the circuit which can cause issues..
Just my $0.02... 👍😉