Mcintosh Speaker cable connection question??

When I connect my speaker cables to my Mcintosh Amp, how do I know which connection is positive & which is negative, it doesn't show a + or - sign n the amp. It has 2 black plug-in with a (c) above it, and 3 red plug ins for each of the 2 channels. The red ones identify 2,4,6 ohms which I understand that part. My speakers do have a + & - on them. Please help....
The "C" is the "common". That is the black wire or the - the other 2-4-6 ohm connection is the red. also Make sure you match the correct ohm connecton.

The two blacks are negative (c stands for "common", sometimes also called "ground") and should be connected to the - on your loudspeakers. The red ones are positive and should correspond to the + on your loudspeakers.

Does anyone know what parts are required to convert the screw type spade/ring terminal wire output speaker connections on a MC225 to a banana style connection, and if that's a smart change acoustically?