So sub or not to sub

Simao, try placement of the sub between the speakers and a little ahead of the plane their on.

I have a pair of Verity Parsifal Encores and a Rel Stadium III sub. I've had this system for a couple of years and haven't changed anything. I do on occasion turn off the sub, and sometimes will only play the monitors and let the lower cabinets remain as stands. All different sounds with different qualities. The midrange and staging sound the best with only the monitors. That's in my room.

Room treatment is important when adding more bass because you have additional waves moving around at different frequencies competing with the mains or monitors. I say go for it especially if you like low frequency sound and "movement". Even more if you can treat the room.

I run B&W 804S full-range and two Rythmik 12" subs from line level signal. I used to have a REL Storm III. The 804 + REL sounded better than 804 alone. The setup with the two Rythmiks sounds a lot better than with the REL.

The key is setup: multiple bass sources provide a smoother bass response. Google Dr. Earl Geddes and his theory and multiple setup approach. Very useful!
The Rythmiks provide a level of tuning the REL just does not provide.
Another key is using measurement software (I use REW) and a measurement mic to test multiple room responses from different sub locations, crossover frequencies, gain, phase, etc. Each sub has it's own tuning, so not a trivial task if you plan on evaluating by listening only.

All in all, in my book subs are a must have. Still wondering about hi-passing the speakers so to avoid having them and the speaker amp reproduce the lowest end they really aren't suited for handling (I use tube amp). On the other hand, two additional bass sources smooth out the response further. I guess we get to pick our poison.

Cheers!