Dynamic external microphone not working with X40

[pktr5]

Hi all,
I would be very grateful if you would have any suggestion that could resolve my problem with a dynamic microphone on my X40...

I have two external microphones - a Shure SM58 clone (dynamic, 150 Ohm) and a crappy $5 mic, probably about 2 kOhm (I didn't measure it). The Shure clone has a 3-pin XLR connector and a cable ending in a 3.5 mm stereo jack, whereas the $5 mic's cable ends in a 3.5 mono jack.

Both microphones work perfectly with the roommate's X61s. But with my X40, the Shure clone results in almost no signal (using the "MIC boost" driver option, there is some weak signal buried deeply in noise). However, the $5 mic works perfectly on the X40! (So does X40's integrated microphone.)

Any ideas why X40 doesn't work with the dynamic one? I've tried looking up the sound chips in X40 and in X61s, to explain the difference, but couldn't find anything obvious in the datasheets...

Thanks!
Pavel