P3 to Subwoofer. Mono or Stereo 3.5mm

[Ccw71+]

REL HT/1003 arriving today. It has a single Low Level RCA input. I am using V3 monoblocks fed by a P3 pre amp.
The Stereo Aux Out on the P3 is recommended for the connection to the Sub. To feed the sub, can I use a Stereo 3.5mm to female RCA adapter plug. Will this sum the L&R or will it short them potentially causing problems?

Adapter plug -

https://www.amazon.co.uk/C2G-3-5mm-Stereo-Female-Adapter/dp/B002DWAXMI/ref=asc_df_B002DWAXMI?mcid=43d56edbbfd73a3b8bb0e36974176deb&tag=googshopuk-21&linkCode=df0&hvadid=696452133743&hvpos=&hvnetw=g&hvrand=4599102995780495546&hvpone=&hvptwo=&hvqmt=&hvdev=m&hvdvcmdl=&hvlocint=&hvlocphy=1007340&hvtargid=pla-444637685510&psc=1&hvocijid=4599102995780495546-B002DWAXMI-&hvexpln=0&gad_source=1