Do you adjust your subwoofer

@liquidsound 

You bet. IMHO 1 sub is a waste of time. I tell people to hold off until they can get two. No matter where you put one sub in a room you are going to get very lumpy bass as you move about the room and it will change with frequency. Within 6 feet you can go from too much bass to no bass. Two subs smooths this out and the more subs you add the smoother the response gets. I just went from four 12" drivers to eight 12" drivers. The larger the surface area used for low bass the lower the distortion, Getting down to 18 Hz flat is not easy. It requires a lot of driver and surface area. My system is up 6 dB at 20 Hz. It returns to 0 dB at 100 Hz. This gives the effect of a live performance at less than tinnitus inducing levels.

@liquidsound 

That is probably where the sub is best time aligned with your main speakers. With digital bass management you can put the subs anywhere they produce the best bass and time align them digitally. 

 I also use full range drivers (ESLs). Are you familiar with Doppler Distortion? If a car passes you with the driver leaning on the horn just as the car passes you the horn changes pitch. Unless there is a large capacitor on your full range drivers they are still moving to low frequencies even if they can not project them. They are moving towards you then away from you and just like the car they are Doppler Distorting all other music they are carrying which for people like us with full range drivers is EVERYTHING! Putting a high pass filter (the other 1/2 of a two way crossover) on your full range driver lowers distortion and increases headroom dramatically. It is not a subtle difference. I cross at 100 Hz 48 dB/oct. It does require a leap of faith because the only way you can do slopes this steep without causing problems is digitally and many audiophiles are also digital phobic. I have been using subwoofers since 1978 and it was a love/hate relationship until digital signal processing arrived in the mid 1990s with TacT Audio. Conversions back and forth in 192/24 digital are sonically invisible. Once you are in numbers you can go almost anywhere you want without any added distortion. Once you have everything set up as you want it you convert back to analog as the very last step.

There are other advantages besides sub management. High resolution EQ is one. We locate sound by volume and phase. If a sound is louder in the left channel you hear it to the left. The problem is that not two identical speakers have exactly the same frequency response curve. Put them in different locations and their curves can be wildly different. I just measured a set of Magico S7s that were down 8 dB at 500 Hz in one channel! What do you think this is going to do to the image? With digital EQ you can adjust each speaker's response curve so that the channels are identical producing the best image. It is way more important for the curves to be identical than flat. 

@liquidsound 

You are on the right path. Might I suggest a second subwoofer and a complete two way crossover so you can put a high pass filter on your main speakers. This will lower distortion and increase headroom dramatically. This is just, if not more important than the added bass a subs brings to the table. This is especially true with full range drivers. The second subwoofer will smooth the bass response throughout the room a little better. Subs perform best up against the wall and in corners, but in order to time align them with the main speakers you need digital bass management. 

I would also like to suggest that every audiophile should have a calibrated measurement microphone and program. You will never know what your system is doing unless you measure it. A good program will also give you group delays which will allow you to integrate the subwoofer better.

It is also important to note that the low pass filter supplied with most subs will never integrate a subwoofer to maximal effect. This requires a complete 2 way crossover preferably digital with room control and delay capability (digital bass management)

Removing the low bass from the main speakers increases head room and lowers distortion. It is like doubling the power of your amplifier. 

A proper sub system is a set it and forget it item. I use my system for theater also and I never change settings for theater. The proper adjustment is proper for everything. 

@crwindy 

It is not personal at all. The settings for music and cinema should be exactly the same if a system goes down low in the right manner. One uncorrected REL 510 is already 6 dB down at 20 Hz. Getting it flat down to 20 Hz would require quadrupling the power. Studies have shown that the most satisfying curve for sound reproduction in the home environment boosts bass up 6 dB at 20 Hz falling to 0 dB at 100 Hz then flat out to 1000 Hz with a slow roll off with 20K down 6 dB. This would require 16 times the power in a REL 510.  In order to get this right you will need another 510 and a digital 2 way subwoofer crossover such as a Mini DSP. You would crossover between 80 and 100 Hz with a steep slope like 48 dB/oct then you can get the correct boost with the gain control on the woofers. I listen to an acoustic bass go down the scale and expect to hear each note at the approximately the same volume factoring in room acoustics which can be a little tricky. But, if the bass gets continuously louder as it goes down, the volume is too high.