Beats are not longer made by Monster and if you listen to the Monster Inspire headphones (in passive mode) you'd realize you are mistaken to dismiss the company so readily. I know I did, but after listening to the Inspire the company has my grudging respect. Beats are what they are, a running joke. I would 100% expect flat response to be an engineering goal and a marketing theme for most high-end gear.
Would second the Monster comment. Plus -- if your patient, you can get some very good deals on their IEMs.
My blue iSports were $29.99 from TigerDirect and I really like them for working out...excellent sound signature for working out, stay put very well, and sweat resistant.