Input levels on mic jack

I have a new HP Pavillion dv9308nr laptop. It seems to have an issue with the mic input levels under Mepis. The laptop has an nVidia chipset, and according to kinfo:

Audio devices:
0: CONEXANT analog (DUPLEX)

lspci says:
0000:00:10.1 Audio device: nVidia Corporation MCP51 High Definition Audio (rev a2)

kmix says:
HDA NVidia

The laptop has mics built into the lid and has a jack on the front for an additional mic to plug in. KMix has sliders labeled Ext Mix and Int Mic. Through experimentation I've been able to determine that Int Mic is for the mic jack.

The problem I am having is very low input levels. The built-in mic never gets above the noise floor even with the sliders at max. I get slightly better results with the mic jack: using a stereo headset mic (3 rings on the plug) I get basically nothing but noise. With a mono headset mic I can get sound, but it's very noisy and low quality, not much above the noise floor.

Both headset mics work very well under Vista, so it's not a problem with the mics or with the jack.

I've played with all the settings in KMix and nothing there helps.

I suspect that the sound driver has the mic levels set way too low. Is there a way to gain up the base settings or range at a lower level than KMix?

kumar