In order to determine which is the right channel output, and which is the left channel output from your B&O 2000, simply plug the black B&O output into your red RCA phono input, the gray B&O output into your white RCA phono input, and listen for the traditional left channel filled with the high register first violin section of a classical symphony orchestra. The right channel usually has the lower register sound of bowed stand up basses.
If there is the massed violin section in the left channel, you have made the correct choice. Otherwise, simply reverse which RCA input jacks you use, and the massed violins should be heard correctly in the left channel.
If you have a "test" or "set up" vinyl record, it always contains one track which will announce something like "you are now listening to the left channel" with a different track announcing the right track.
Many times, when re-positioning equipment, and re-attaching wires, the left channel, and right channel get reversed, and it may not immediately be heard with small group jazz, or pop selections, unless the placement of performers memorized.