For lowest parasitics, a P-Pchannel JFET works very well. A gate to source capacitor, like 470nF and a very high impedance pull-down on both drain and source, like 1Meg. You should AC-couple the source leg through a sizable cap, sized depending upon your impedance on the input side, maybe 220uF just to prevent phase shift and low-frequencies from attenuating.
The gate itself is driven also through a 1Meg; it requires no pull down. Depending upon the gate threshold, you can turn OFF (OPEN) the drain-source signal with a positive voltage (greater than the gate threshold voltage).
Operation:
During conductance (gate at 0V or floating) the audio signal will couple through the gate-source cap and thanks to the 1Meg gate resistor,the gate and source will track, meaning the transistor stays in conductance (Vgs = 0).
When you introduce the OPEN gate control voltage, then the gate sees the signal at a DC offset, thus Vgs = Vcontrol + Vpp audio (not to imply that the audio signal is required for operation). HOWEVER, your gate threshold voltage must be greater than 0.5|Vpp| of your audio signal, such that when it goes negative (due to AC coupled source, or drain -- this is a bidirectional switch) it will not pull the gate below the threshold voltage you are using to control it.
Alternatively, you can make your gate control voltage higher, but be careful not to blow the gate, and, for digital control, high-voltage may not be a straightforward output option.
That's a discrete solution. The SSR options are very well covered for RF, and audio frequencies, with pF of parasitics and 1 to 25 Ohms of on resistance (you can choose betwen higher parasitic capacitance and lower on resistance, or vice versa, depending on the application -- RF cares much more about parasitic capacitance).
Look into Panasonic PhotoMOS relays. Their latest TSON pkg device is amazing, but only available in N.O.. But these sport a 40uA to 1mA turn on/off requirement, and can pass 30VAC to 600VAC. Their other PhotoMOS are actual LED photomos devices; the ones in the TSON pkg are not, yet they still call them PhotoMOS. But they are not regular MOSFET switches -- gate control is an oscillator through a diode bridge, cap and regulation circuit. The point being to completely isolate the switch from the input control, but in a clever way that only requires 40uA to generate Vgs.
As far as what series resistance you can handle, that has to do with any RC parasitics and input impedance, as well as driver impedance. If that is not high and low, respectively, then no lower series resistance, even 0 Ohms, will help recover the losses. So normally, your output driving impedance is a few Ohms, and your input impedance is high, like 10's of k Ohms or more. So 25 Ohms in the path is negligible.
