What do you guys think of adding a subwoofer to this system?

The most important part of extracting great performance with subwoofer(s) has been touched on by a couple of others. It is not only proper integration with your main speakers, but more importantly, with your room. Getting bass "right" can be challenging due to how the room reacts when adding a subwoofer or subwoofers. Proper phase setup along with physical location in the room relative to your mains and listening position is critical. Getting that proper integration can take days or even longer with experimentation of not only the settings on the subwoofer, but also its position within the room. Even moving the subwoofer a foot in one direction or another can have big impacts on peaks, nulls, "boominess" etc.

But with patience, it can lead to a whole new experience.

only a rocker needs loud noise, nobody else does not need a sub .

@jim5559 , Listening to 95% of the subwoofered systems out there I can understand how you would have that opinion. Most people only go 1/2 in when they get subwoofers. If you are critical it has to be an all or none proposition. To do this correctly you need at least two very sturdy subwoofers, digital bass management including selectable crossover points and slopes, phase and time alignment and room control, at least 1000 watts/subwoofer and decent room acoustics. If you could hear a system set up this way your opinion would change. Shoving one sub under a system with nothing but a low pass filter is a sure recipe for inferior sound. Doing it the same way with two subs is also a dismal approach. You are correct in stating there is a music preference for this kind of an approach. However, listening to a large symphony orchestra through a big system with SOTA sub bass is a thrilling experience.

I've had sub(s) for many years now and highly recommend them.

Having said that, sometimes I've found it really difficult to integrate them to the room.  I purchased a miniDSK UMIK-1 calibration microphone and the REW (Room EQ Wizard) software to help integrate the subs with the room and full-range speakers.

In our last house, my listening room had terrible bass acoustics, eventually I had to install 10 bass traps to tame the extraneous bass the room added to the music, and could have used more, but my wife was referring to that room as my "padded cell".

We moved to a new home and I had a customized listening room done as part of the build and I'm loving life in the new digs!  This room has some sloping intersections of the walls & ceilings (a good thing in my case).

I have a pair of JL Audio F113V2's (otherwise known as "overkill") and one of the sub's amps died, and while the amp was being repaired by JL Audio I was not a happy camper, as I not only missed the little bit of bass augmentation, I mainly missed the "visceral" experience that the subs add to the music.

@mijostyn +1. You nailed it, as did the @ejr1953  using calibration mic and software

I finally sold a 10+ YO pair of SVS powered subs; an Ultra and a Plus (the tall round cylinders). I was never able to get a seamless blend, mostly due to the volume control settings being too coarse, virtually impossible to dial in. In fairness they were not designed for quality 2 channel systems. May be better now, but...

One of the biggest issues I had was because polarity on many discs is out (especially with greatest hits, or multi- recording studios) compared to the rest of the frequencies, and while they have phase/polarity adjustment, it is manual. IMHO, having remote control over volume and polarity is essential to get seamless blending. IMO to achieve great sub bass, you need a separate beefy amp + active XO=$$$$+ SIGH