We are starting to see various hybrid headphones and now IEMs coming on the market. I enjoy my hybrid dynamic/BA Final Audio Sonorous IV headphone. PSB Speakers has now released the first hybrid dynamic/BA IEM, the M4U 4. Peter Pailis posted a review of the M4U 4 on Headphone.guru. Peter believes that at $299 the M4U 4 is the best IEM under $600.