Specifically for fps and shooters I would recommend a iem with a decent amount of sub bass. Mids and vocals in the iem can pick out the vocals and more of the even toned sounds. Highs/airs can pickup the sharper sounds. You dont need to shell out a crazy amount for decent performance. 7hz salnotes zero is fantastic $20 iem that has a balanced sound profile that pickup on footsteps pretty well. So with a more balanced sound, its eaiser to look at everything on a similar floor and pinpoint. If you want a more expensive personal recommendation then tangzu wu heyday is a very good choice. I recently got to demo it, it has a fantastic open sound with even body and tonality. The bass is alot more realistic and has a clean tighter feel. There enough sub bass to pick up on even the smallest sounds. Heres a demo on it.