Rather than figuring out which headphones will be louder, I would focus on finding a pair of headphones with good isolation.
This is where sounds from outside are blocked out so that you can’t hear them, meaning that the headphone volume doesn’t need to be as loud for you to be able to hear the music coming from them.
Simply turning up your headphones is very dangerous for your ears – you will damage them over time and many DJ’s have tinnitus in one or both of their ears due to having the volume too high. You should really be wearing ear plugs whilst DJing to protect your ears..
I suspect that the reason you are struggling is 1) Those numark headphones are frankly just rubbish and 2) Studio headphones are not designed to block out the sound from outside – they are more focused on an even frequency response than blocking out external sound. As there doesn’t tend to be much external sound in a studio..
I would look at a decent pair of DJ headphones. I use Audio-Technica ATH-M40x headphones, which I really like – but there are lots of alternatives.
There have been a few threads recently on this, so try using the search function in the forums for other ideas 🙂
bob6397