Unfortunatly only one ADC DAC Pi can be used on a Raspberry Pi as it uses the SPI bus which only supports up to two SPI devices. As the ADC DAC Pi uses one channel for the ADC and the other for the DAC there isn't any easy way of adding any additional devices to the bus.
The closest ADC board we have based on your requirements would be the ADC Differential Pi. It has 8 channels on each board and a differential input of -2.048V to +2.048V but the maximum sample rate is 240SPS in 12 bit mode so that will probably be too slow for your project. The 240SPS is also the maximum rate when reading from a single channel. If you are switching between channels then the sample rate will be lower as there is a small delay when changing to the next channel.
As the ADC Differential Pi uses the I2C bus it can be stacked with up to four boards on a single Raspberry Pi giving you a maximum of 32 inputs.
We don't have any 8 channel DAC boards at the moment.