Speakers replace or improve?

fletcher munson 'loudness' curve(s)

we hear less bass and less highs as the volume lowers.

Fletcher Munson Filters (named 'Loudness' (a stupid name, it should be called 'Low Volume Boost.

As you lower volume from your normal listening level: 'Loudness' PROGRESSIVELY boots the bass, leaves the mids alone, and boosts the highs.

Your manual suggests a different solution, by progressively cutting the mids, it 'in a sense' creates the same result. This method might be good for low powered amps (that would distort trying to boost bass), and/or inefficient speakers that need more a lot of power (or a combo of both).

IN any case, you do not cut the highs.

IN any case you do not alter loudness by -30db

This is why I think this is a JOKE.

That open area is going to cause loading problems. You really need to buy a couple of good subs that will proplerly load that whole area. Which means to get good bass you need something that will really move a lot of air. Forget the cheaper subs, they are not going to cut it. That is a larger area you are trying to bass load. Do you have a friend you who will let you borrow a couple of large subs so you can try it out?

No, I don't have a friend who can let me borrow his sub. But when I turn on my sub it produces more than I need bass. I just need to learn how to use it properly because it has two knobs and two switches. 

I was trying to avoid using the sub because I can't put it in front. It sits close to the right side wall. But it looks like I need to use my subwoofer all the time. And probably buy a second sub. 

My sub allows wiring speakers to the sub. Is this a good option? Right now my speakers wired to the amp and the sub connected to the amp.

@sukhenkoi I think you need to step back for a minute. It looks like you are all over the place with trial and error. What you are experiencing is very common when folks have home theater gear and then want a taste of High Fidelity. Good for you. But you need to start over and approach things a little differently.

Going back to the original set up in your opening post, you say that CD sounds good. That means your system is functioning at a basic level. If this is the case, then the issue is with the vinyl source.

Is that correct?

No, I don’t have a friend who can let me borrow his sub. But when I turn on my sub it produces more than I need bass. I just need to learn how to use it properly

There should be a knob on the sub’s back called crossover. Set it to 60 hz or so for now.

There should be another knob on its back called volume. Ya crank it counterclockwise until there’s no too much bass...and the sub’s bass feels like it’s coming out the speaker, not the sub. In other words, the sub should disappear and the speaker should sound like a non-flaccid bass capable speaker