If you get a monitor with multiple inputs, you can just use the DVI for your computer and VGA for the console, no need to have a switch you just switch inputs on the monitor.
For the speakers, I have speakers with line inputs so I just run it in there.
Otherwise you can probably just get something like this:
And then a male to male RCA adapter. Or if they make a female stereo 3.5mm to female stereo RCA.