Yo Frank of Number 1:
AUX = Auxilliary, spare, extra, available ins/outs.
So, you can patch a CD player into/through an AUX or a radio or a wax turntable or a processor. Can't patch through a dry martini. That needs to be made to order.
If you had an integrated amp, the CD plug in is just another name for AUX except the circuitry could be high quality for CD.
I hope this AUXED you.
Green Hornet