Why I'm not adding a sub to my 2-way monitors for music

Its all room and speaker dependent and room treatments and speaker placement.  I was going crazy with measurements.  I was able to get the Fritz Carrera Be to play -3db at 20hz and damn near flat from 23hz to 100hz in my last house.  
 

Its so room dependent and speaker placement dependent and if you aren’t taking measurements you’re pretty much shooting in the dark.

You definitely were on the right track by avoiding boost and cutting the peaks.  

Just curious how close your speakers are placed near the walls?  

I am not a total sub fiend but even though my mains go to 45Hz as measured, the two REL T9i I have provide the dynamics, impact, sustain, texture and hall ambience that make a big difference for me and my system. The  RELs are more subtle and musically accurate than other subs I have tried as well as being easy to integrate and they avoid coloring the midrange- all reasons why I like them so much.  

I own stand mounts as well as floor standers ,and by asd8ng a subwoofer - A Quality one ,two even better more even bass , the bass fundamentals just donot effect the low frequencies ,but also up into the lower midrange .

when setup properly the music as a whole is much more substantial as music 

as a whole .i  have been into audio for a long time and owned a Audio store fir 10 

years  and have had the opportunities to compare most every type of Loudspeaker type ,and setup in rooms . Whst ever you do is totally up to you ,but there is ample proof out there 1-2 subwoofers of respectable quality is a win win ..

svs 3000s has a great app to find tune your system , JL  Audio,  Rel , Kef , and several others are verygood.

Well obviously this is your opinion and your room with your speakers.  It may work for your system but that in no way guarantees the dame result for someone else.  Lately I have been reading too many opinions, etc., that are somewhat useless for other people's systems.

Happy Listening.

Adding subs is always an improvement if crossed over right. But each person has to decide if the cost, space and complexity is worth it to them.