so I guess I will have to figure out how to feed it from the same power as the arduino for this to work out, right?
No separate power supplies are fine just connect the grounds together, see:-
http://www.thebox.myzen.co.uk/Tutorial/Power_Supplies.html
Also, will connecting the analog input to the same pin that speakers connect not interfere with the sound volume/power of the speakers?
No the arduino input is so high in impedance there will be no extra load.