Your ohm meter will not give you an accurate reading on a speaker.
It looks like the PL-300 is at lowest, 4 ohm stable. If it is a 2 channel amp (which
I believe it is) drive each speaker with a separate side (Left and Right).
You may damage the amp if you parallel or series the speakers.
7Here is a great site for all electronics info. See #57 on the right side pane for more speaker info.
Basic Car Audio Electronics Site