If you leave the 1050 on Surround mode, it will detect the signal and play Dolby Digital, DTS, DPL or mono, depending on the input.
The Natural, Jazz, Stadium... modes are digital signal processing (DSP) modes that mostly just don't sound good to me. They use time delay effects to give the sense of space.
Other than surround, the only other mode I use is Stereo, for the occasional time when I want it straight. With my front speakers (Spica TC-50) it gives the best imaging.