If I read you question correctly, you already have the digital part worked out: you have switches connected to a mcu (pic/avr?) and the mcu connected (via usb) to your pc and the pc will sound the audio-clips, right?
Now, you have probably connected both the mcu and switch to a low voltage (5 volt) power supply. When you flip the switch you'll get 5 volt input on one of your mcu's gpio-pins's right?
Then you need to know first how much amps each powerstrip should be able to supply (per switch). The (solid state) relay's should be able to provide at least this much current!
Next you need to make a choice: mechanical relays or solid-state-relays (rated for AC).
Solid state relay's do not require as much power(amps) to hold their contact then mechanical relays. This is because they only drive a led aka opto-coupler (providing isolation), thus it needs only 2 to 15 mA. But they MIGHT interfere with your appliances plugged into your power-strip. Check their datasheet how much current they require (and their max current) and check their max/min input voltage.
Mechanical relay's provide the exact equivalent to a mechanical switch, so it can not interfere with anything it is powering. BUT they need more current to hold their contacts due to their coil. 500 mA is a nice figure and three of them means you need at least 1.5 amps (apart from the current that your mcu draws). Lastly for a mechanical relays you need a reverse protection diode across the coil (a lot of relay's have them embedded, so check this!).
As you can see, the choice solid-state vs mechanical relays also effects how much power your power-supply needs to deliver.
Suppose you have mechanical relays that can switch 230 vac @ rated current (you need) with a 5 volt coil, then you could simply wire the relay's control-input in parallel with the mcu gpio after your panel-toggle-switch.
In other words, if you flip the toggle-switch the 5 volts go to the mcu and to your relay's enable input.
The same goes with the solid state relays (don't forget to work out the correct resistor value to supply the optimum current to it's opto-coupling led)
If you have a mechanical relay with a coil-voltage higher than those 5 volts then you could use an opto-coupled driver for your relays. This would also mean your powersupply needs to supply 2 voltages (although you could use a drop-down regulator for the mcu-part and have the powersupply deliver just 12/24/whatever volts that drive your mechanical relais).
Hope this helps!
As a side-question: how did you manage to get the difficult part (mcu usb pc-drivers) to work and get stumped on something like a relay?
