Hello Wonni,
Glad to hear you have successfully used the AFE5808 in your US application already. Having come from using the AFE5808, switching to the AFE5808A will be very easy. AFE5808A is an enhanced version of AFE5808 and it is recommended for new designs. Compared to AFE5808, it expands the cut-off frequency range of the digital high pass filter; increases the handling capability of extreme overload signals; lowers the correlated noise significantly when high impedance source appears.
Gain matching is specified as channel to channel and device to device. Gain matching specification describes how closely the gain of one channel matches the other channels in the same device, referring to page 7 of the datasheet, under Gain Matching (Channel-to-Channel). Typical channel to channel is +/-0.25dB. Device to device, the gain match is typically +/-0.5dB.
The various modes (low noise mode, low power mode, medium mode) allows you, the designer, to make an educated decision between low noise performance and power, among other things. You can pick where that happy median is for your system. Simply speaking, the lower the noise figure, the more power you have to burn. The details of the trades off are listed in the datasheet and too many to post here.
Hope this helps.
Regards,
Lijoy