How to Connection Focal Sub 300 P

I have a Focal Sub 300 P with high level inputs (via the speaker cables) and low level via RCA from the pre-amp.

I have a NAD 3130 amplifier. The pre and main amps are connected with U shaped metal jumpers.

If I remove the metal jumpers and make the connection of the Sub to the pre-amp, do I restore the connection between the pre and main amps by using a splitter cable from each channel, ie one side of the splitter to the amp and one to the Sub for each channel?

Alternatively, it has been suggested I connect the Sub by RCA to the Tape-rec out channels of the amp. There would be no volume control between the amp and the Sub.

Any comments on how best to make the connection: Hi level with the speaker cables for either of the Low level?

Speaker level is the cleanest option for you and to my ears the best sounding.