Aragon 2002 Pre amp to a Monitor Audio subwoofer

I have never used a sub with this setup but am doing so now. Can I use a 2 male to 1 female Y adaptor on my preamp out and run a single RCA to the subwoofer?
Or do I need to run 2 RCA's out? I know it is a monaural signal. My Monitor sub does have 2 inputs - but if can can use one RCA - that be be mu choice.

Thanks