Subwoofer connection to Luxman R-117?

https://www.lifewire.com/connect-a-subwoofer-to-receiver-or-amp-3135132

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What is the Paradigm Sub's full model #?

I would like to know the sub's options if any. The sub's 3.5mm male: is it mono, or stereo? Is it possible that the sub's 3.5mm is actually part of a cable that has been connected to the sub (thus removable?)

Main speaker's model #?

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Are you

#1. simply adding an independent self-powered sub to your system? amp (in your receiver) still boosts ALL frequencies, and main speakers still reproduce ALL frequencies.

or

#2. are you going out to the sub first, using the sub's crossover, sub's amp takes the low bass; sub sends upper bass, mids, highs back to receiver (via receiver's 'main in'?). This removes the need for the receiver's amp to boost lows and the main speakers to reproduce low bass.
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That Luxman has quite a few options (more than most) to go 'line level' out to a sub. all rca jacks, all pairs L and R.

two pre-outs:
a. upper pre out to sub (no removable jumpers) (for #1 above)
b. lower pre-out (remove jumpers), pre-out to sub, then after sub's crossover back to receiver's 'main in'. (for #2 above).
b. tape loop out/back in
c. signal processor loop out/in.

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Yes you can combine a pair of RCA to a 3.5mm stereo female, then insert the sub's 3.5mm stereo male (if it is stereo male).

https://www.amazon.com/UGREEN-Adapter-Compatible-Smartphones-Tablets/dp/B00B2HP1FY/ref=sr_1_5?dchild...

However, is the sub's 3.5mm mono (1 black stripe) or stereo (2 black stripes)? (l & r would be converted to mono inside the sub)

Thanks so much for taking the time to offer direct advice and clarification
Full sub model is Paradigm PS1000 v3. 
Upon further inspection I discovered I am  technically inept. I errantly described the cable I explained in original post. The interconnect cable actually is 2 rca male that start at the subs Low Level Input and  Output from sub out, life out or pre out and this 15ft thick insulated cable terminates with a single hefty rca male ( that I used to insert to the dedicated subwoofer out on my old Yam Rx-V800. I appreciate all these options I did realize existed. If I am understanding what you shared above I can take the easy button And insert the single rca male into either of the top pre out??  Or buy the adapter you mentioned as to enable left right info in conjunction with / a set of short rca cables. 
Or just replace the heavy duty cable and use a set of long enough 6 ft) RCA 2 make to 2 male and directly connect the devices. 
I do not think I am ready (yet) for option 2 and any of the three suggested  connections. (as of today) 
my main speakers are the ADS 780/S2 which do not seem to need the sub but I have 3 smaller speaker sets in a closet that would need the sub. Mission 502, B&W 685 (not S2) and Pioneer Elite SP EBS73.