Download PowerAmp and it has a built in 10 band eq.....Dolby atmos is great for videos but not so much for music. Dolby Atmos works with PowerAmp sometimes if you want more customization,but sometimes not. Another great player is Neutron and it has crazy good audiophile settings and DOES work with Dolby Atmos.
I also use Power Amp. Set the equalizer in Power Amp to your liking. It sounds much better than Dolby. I think the whole Dolby thing was just a marketing gimmick just like Beats with HTC years ago as well as Apple.
That is one of the more annoying limitations of the dolby atmos software. Those limitations are set by Dolby, and the phone makers don't really have much control over it.
Many license the software because they have special ways of reproducing some of the harmonics related to lower frequencies that the speakers may not be able to reproduce,this in turn offers the perception of a better bass.
Most higher end headphones can get by with no EQ, but if you have one that needs EQ, and have a microphone that can do the full human hearing frequency response range, as well as have your mic characterized and calibrated to give a flatter pickup using the EQ in an audio editor, then playing a frequency sweep over the headphones, and then seeing which general bands need to be increased or decreased, and then make adjustments the best you can in order to get a flat response from the headphones.
Beyond that, if you are not looking for a response that is as flat as possible, then just tweak them until it sounds good.
5 bands is limited, but if split and average the adjustments needed into 5 chunks, you can get some really good results out of it.
PS, for Dolby atmos, in the music profile, disable the volume leveler, I have a feeling that many of the quality limitations some users experience with it, is due to the volume leveler.