Hi Bailin,
Look at the ADS1278 and ADS1274. These are 8-channel and 4-channel (respectively), 24-bit simultaneously sampling delta sigma converters. Meaning, there is a delta-sigma modulator and filter for each channel instead of a multiplexor that shares multiple channels with one modulator. Those devices can daisy-chain their SPI communication, but you'll need to consider the data rate and your SPI clock to make sure you're able to read back all of the data before the next conversion cycle.
Other options would need also need multipIe ADCs to meet your requirements. The next closest single device solution would be an ADS7952, but this is a 12-bit SAR ADC.
Do you have any target performance specifications? (SNR, ENOB, etc...)
Regards,
Chris
