Sub for stereo receiver?


I've received different answers to this question, which I thought was basic. Admittedly, being new to audio, I know little about a lot,. But I have a Luxman R-115 stereo receiver from 1990, and would like to add a sub. The unit has two Pre Out jacks. So I asked around, contacting a local dealer, a speaker company, an audiophile friend; I also spent too much time trying to find an answer online. Maybe I just don't know where to look. What I heard:

1. One guy told me I can run cables from a sub into the speaker terminals along with my main speakers.
2. Another guy said just run cables from the sub into a Pre Out jack.
3. Another said that I should probably ditch the plan and get something that would allow me to hook up two or even four subs.
4. Another said some things I still can't understand.

I'm a simple man, and mistakenly thought this was a relatively simple idea. My bad. But I'd still like to get something to enhance my listening enjoyment, without having to buy a new power source and filling the living room with subs, and without needing to understand what bass management or DSP based EQ means. Forgive my naivety if you must; help me if you can, remembering that the simpler the explanation, the better. Thanks. 
anton99
Me, too. I'm partial to Col EH Taylor bourbon, so maybe I'll be "The Colonel." Sounds pretentious, but in a genteel way.

At any rate, E or Nigel, thanks for the suggestions. I'll check out JL Audio and see what they have. Not while sipping, though; that's how I ended up with my last DAC and (superfluous) set of bookshelf speakers.
I think I need a pseudonym...or at least a stage name.  I will ponder this over an adult beverage this evening.
OP:  Nigel is my pseudonym.

Any sub will pair well with it, the question is what will pair well with your speakers, room and room treatment.

We can be audiophools all day and talk about sublime essence of bass notes, but the reality is that the biggest hurdle you will need to overcome is setting up the subwoofer correctly.

JL Audio makes some of the best auto integrating subs, at an  unbelievable price tag.

Best,

E
1. One guy told me I can run cables from a sub into the speaker terminals along with my main speakers.
Some subs can be connected this way.
2. Another guy said just run cables from the sub into a Pre Out jack.
This is best. Your receiver has 2 pre-out jacks. Use either one.
3. Another said that I should probably ditch the plan and get something that would allow me to hook up two or even four subs.
You already can hook up four if you want. So your plan is fine.
4. Another said some things I still can't understand.
With audiophiles this is what we call situation normal.

I'm a simple man, and mistakenly thought this was a relatively simple idea.

Yes. But audiophiles love to make everything as complex as possible.
My bad. But I'd still like to get something to enhance my listening enjoyment, without having to buy a new power source and filling the living room with subs, and without needing to understand what bass management or DSP based EQ means.

One sub will do you just fine.
Forgive my naivety if you must; help me if you can, remembering that the simpler the explanation, the better. 
Any time.
Erik—

Thank you. The article is helpful, and confirms a few things I've heard. Did you read this before or after you added a sub/s? 

Any suggestions on what sub pair well with the Luxman R-115?
I have a Luxman integrated, so lets assume it works the same way. :)

The nicest way is to use the pre-out jacks to your sub.

Now, as a Luxman and subwoofer fan, I'd like you to read this:

https://speakermakersjourney.blogspot.com/2020/04/how-to-not-buy-subwoofer.html