According to IGN Cube, Factor 5 and LucasArts have announced that the previous hint about 5.1 channel sound was indeed referring to Factor 5 utilizing Dolby Pro Logic II encoding in Rogue Leader.

While many gamers won't be able to experience the new sound today (DPLII requires a new reciever capable of decoding a DPLII signal), it is nevertheless a great option for gamers with money to burn to experience an incredible surround experience from their GameCube.

Dobly Pro Logic II is similar to Dolby Digital 5.1 in that there are six channels of sound ... five full-frequency channels, and a LFE (low frequency effects) channel. While Dolby Digital has advantages over DPLII in separation and cleanness of sound, DPLII doesn't have the latency issues of Dolby Digital.

The best part about DPLII is the relative inexpensive nature of it. Since it is sent along a standard audio stream, regular stereo cables (your red and white RCA plugs) will do fine. While it will require a special decoder, you won't need optical or digital coaxial cables, or a more expensive receiver to decode the signal.

GameCube owners without DPLII hardware can still get some surround effect. DPLII can degrade to standard Pro Logic ... however the sound fidelity will be compromised.

IGN Cube has impressions of the DPLII soundtrack in Rogue Leader ... check them out.