You have limited I/O on the Arduino but if you don't need to do much else 8 in and 8 out are possible. Analog I/O is even more limited but to control switches or read buttons it's not needed and can act as digital I/Ohttp://www.nxp.com/pip/74HC_HCT4316_CNV.html
You can use 8 of the Arduino digital outputs to control 8 channels on two chips. If you're feeling frisky you can use a serial in parallel out IC and get less I/O pins to control 8 OR MORE digital outputs which will control 2 OR MORE quad bilateral switches. You do have to match the signal you want switched to the quad bilateral switches.
If this is for analog this will work well. If it's for something simple like 'on/off' then you can use the Arduino pins or the pins driving a transistor or the pins driving a transistor driving a relay.
When switching some signals with relays you will need to do a bit of research as switching high power audio tends to cause blown amps.
Messing with household AC can be lethal.
Button inputs are easy and documented. There are examples built in to the development environment.