looks like it could work.
the first link did not show anything about the switch, but closing contacts is not rocket surgery.
Thanks for getting back to me. At this stage I think there are three options.
Safest solution: opto coupler. Search for "hacking buttons". If you have the Starter Kit, it's chapter 15.
+1. opto couplers would be perfect.
A friend has suggested the following but I don't see how it would work?
When mC pin goes low current flows from 5v to mC pin via both resistors. It acts as a voltage divider. At the junction of the resistors the VRX sees 0.5 volts.
My calculations suggest the VRX will see 0.005V.
My calculation suggests 0.5V (µC low) and 5V (µC high). But it's questionable whether this will work with the DIP switches.
In any case you have to figure out the voltage and polarity on the open switches, before you can start connecting anything to them. Do they have a common line on one contact, and is it 0V or 5V or something else on the device?
Using opto couplers you only have to find out the polarity of the voltage on the open switches, and whether the opto coupler output supports that voltage. Eventually the current through a closed switch should be measured as well, but in any sane design it won't exceed the opto coupler capabilities.
There exists another solution, using (Reed) relays. Then you have no problems with voltages and currents, because the relay contacts work independent of logic voltages, polarity and currents.
Just some thoughts and guesses (I haven't used this):
The power supply voltage is rated at 3.5-5.5V, so it's probably connected to 5V.
The 3 channel select inputs would have internal pullup resistors to VCC (5V).
It appears that the channel select inputs are directly compatible with 5V Arduino outputs ... there shouldn't be overvoltage or overcurrent issues. There may not be other issues deal with (interference, etc.).
Perhaps direct connections is all that's needed. Do full testing with a multimeter first.