Hey Don,
I've noticed that many IEM's handle bass better than over the ear headphones, and a lot of that has to do with the seal. I've had some Philips earbuds in the past that really did well with the low notes. The best I've ever had for an in ear, concerning bass, is the Denon AH-C300, which I still use. They handle the low notes just as well as my SZ2000 headphones aforementioned. The difference however is that the earbuds will tickle my inner ear with notes in the 10-50hz range, whereas my SZ2000's will vibrate the glasses on my face, the side of my head, and my neck. On bass tests I can feel the bass down well below 20hz. It seems that I stop noticing the pressure around 10 hz even though the driver is still moving.
The downside to the SZ2000 is they need a lot of power (relatively speaking) and a lot of EQ. I amplify them with a 4,000mw amp on high gain with the gain stage 3/4 maxed out and the volume on windows at 80-90 on some songs (I never max out windows volume). I spent many hours experimenting with EQ settings and have them sounding very good now. I actually used a binaural microphone to record a sine wave and measure my frequency response from which I EQ'd them.