Hi, Gonzalo.
Apology for the delayed response.
I would say it really depends on your application. If precision is the objective, noise must be lowered to obtain a higher peak-to-peak resolution but output data rate is reduced. This is the tradeoff - you gain something but you are also giving up something. You can check Table 5 and Table 6 for the Output RMS Noise Vs. Gain and Output Data Rate on page 12 of the datasheet. It shows that the higher the gain, the lower RMS noise while the higher the output data rate, the higher the RMS noise.
For your input signals, just be sure that AD7705 will receive the correct input range. AD7705 can still work with the input signals you have attached since it has an input range of 3.5 Vpp. But to start with, it is better to apply a DC input may it be a zero-scale, mid-scale or full-scale to check your configuration.
Let us know if your require anything else.
Regards,
Johnny