I want more bass…

What kind of music are U listening to? does it have really deep bass? Most people think mid bass is deep bass. Woofer position, as mentioned , is critical for deep bass. Rooms actually have null spots where there is no bass if your woofers are there. That's the plus of subs. You can put them in the good spots for bass and the main speakers for best sound and it's usually not the same spots. Finally how loud do U listen. It's very hard to hear deep bass at lower levels. The ear frequency response varies with level and is only flat at around 100 dB, too loud for safe listening. At normal loud levels bass is down at the ears significantly. 

Experiment with speaker positioning.  If you you don't have much freedom to move them about relative to corners and walls (closer or farther) then you may be stuck with the bass you have.

A sound level phone app and a source for playing full bandwidth pink noise will validate the best spot for the speakers.  

Once you have the positioning optimized and are still not happy with the bass then it is time to consider other options but you aren't there yet.  

Definitely a fan of powered separate subs.

just moving the subs around had a big impact.

Active crossover, then bi-amp, move sub freqs off of main speakers and amps don’t need to try to push those frequencies either.  For my old ears, I also limit the top end frequencies.  I can’t hear them anyway so why should I have my amps trying to push them? (Personally, I limit high end to 18khz, I can’t hear anything up there anyway.)

i know, I know.. but “I” cannot hear the difference, so I prefer to enhance what I can hear.  
I like it this way.  Seems my amps and speakers do also.

Nobody has asked what the rest of your system looks like. Are you using vinyl as a source? Or are you doing digital?

If digital, make sure your Network is all dialed in, if not, you won't be getting the bass you want. Just a thought. And if you are doing vinyl, and your phono preamp and associated gear is not up to par, same deal.

I have full range tower speakers with built in powered woofers And also have two subs and won't do any critical listening without my subs in the mix