Does the speaker have a separate line-level input for the powered sub?
If so, you will select Small and then route the SUB or LFE line level output from the receiver to the speaker.
If the speakers do NOT have a separate line level input , then the crossover within the speaker itself will split the high and low frequencies between the powered sub and the unpowered mid/hi. In this event, you definitely want to use Large setting--this sends a full range signal to the speaker, and the speaker's crossover then sends the appropriate portions of the signal to the different drivers. If you choose Small, the low end of the signal will be truncated, and the crossover will have no information to send to the powered sub.
If so, you will select Small and then route the SUB or LFE line level output from the receiver to the speaker.
If the speakers do NOT have a separate line level input , then the crossover within the speaker itself will split the high and low frequencies between the powered sub and the unpowered mid/hi. In this event, you definitely want to use Large setting--this sends a full range signal to the speaker, and the speaker's crossover then sends the appropriate portions of the signal to the different drivers. If you choose Small, the low end of the signal will be truncated, and the crossover will have no information to send to the powered sub.