when it comes to amplifier and speaker connections, it is always best to match the impedance (ohm rating) of each part.. ie 8ohm speaker plugged into 8ohm amp output.. but as long as you dont go below the rating of the amplifiers output impedance.. you can connet a speaker to it.
For example - its safe to connect an 8ohm speaker to a 4ohm amp output but NOT SAFE to connect a 4ohm speaker to an 8ohm amp output.. but every time you double the speaker's impedance you will cut the volume output of the amp by ~50%. (8ohm speaker + 4ohm amp is half as loud as a 4ohm speaker + 4 ohm amp)
remember, you can always go up.. but not down.
