In the car this morning waiting for OSWMBO, listening to the radio. Pressed the CD button and started to have a play with the base, treble etc. after pressing the tone button I turned the volume button by mistake and the surround system changed from '3 channel' (which it has been on since we got the car) to 'Stereo' with a noticeable sound quality reduction...still good but not as good as '3 channel'. Rotated the volume button back to get '3 channel' again and then further almost by accident and it showed 'DPL II' on the display and WOW how good does that sound (Also lots more buttons to play with in that setting)
RTFM (Pleather bound - naturally) and on page 229 there it is, clearly explained.
Note to self - No more Vino Tinto whilst studying

I use the 3 Chanell on normal DAB radio and Prologic when watch a movie on the iPhone crank up the bass etc make good watching On a 3" screen  Former Mod/Member, with the most post & Chicken George Arch nemesis