Re: Auto range circuit
Many analog switches and multiplexers CAN pass negative voltages. For example, when a DG508 is operated with dual supplies (±12V to ±15V) it will easily pass ±10V signals, perfect for range selection (i.e., gain or attenuation control). And the 4066 you mentioned can be operated from ±5V power, thus enabling it to pass analog voltages in the ±5V range.
Important note: analog switches and multiplexers are not like mechanical relays in that they have significant resistance when operating in the "on" state. When you use an analog switch to control gain, try to arrange the circuit so that no current flows through the switch. If your design does not do this, you will have voltage drops across the switch that are influenced by a variety of factors and you will not be able to easily calibrate out the resulting errors.