the sound chips is an AKM 4641VN: the same as on HTC_Universal and also on the ipaq hx4700.
see HTC_I2C_IDs for i2c address.
the device is communicated with via i2s (not i2c - that controls the volume etc).
there _does_ exist a pxa-i2s.c driver in 2.6.17, and also a h5xxx pxa i2s driver, but the h5xxx driver is for the ak4535 not the ak4641.
it's all a bit of a mess.
what is needed is a rewrite of ALSA for SoC devices: