Hi Bo,
As you have noted that the AD7760 can get you a dynamic range of 120dB at data rate of 78ks/s, but at the expense of the higher power.
If power and size are constrains in your application, the AD7960 with a flexible serial LVDS interface availalbe in a small form factor (5mm x 5mm LFCSP) would be a better choice and you will have a flexiblity to do the digital filtering in the FPGA. The added benefit of the LVDS interface is that the mutliple AD7960s can share its clock (which can run upto 300MHz), resulting in reduced the number of digital signals and ease of signal routings.
Regards,
Maithil