Lee, I always listen to 2-channel music source material in surround, using DPLII or similar. This releases the surround ambience that was imprisoned in the front channels because there was no place else to put it and sends it to the surrounds where it belongs. When the levels are properly balanced the result may seem relatively subtle, but switching suddenly to straight stereo mode clearly demonstrates the collapse of the sound field toward the front for a less realistic effect.
Commenting on some of your current exploration: the gorgeous Hansen 2d Symphony is a real favorite; Piston's The Incredible Flutist is a must; all of the Vaughan Williams symphonies are loved(two complete sets with Boult and Handley plus individual discs with Bakels, Barbirolli, Haitink, Previn and Slatkin); The Elgar 2d Symphony is his finest work in my view; besides numerous copies of Holst's The Planets, his The Perfect Fool has to be included. One set of American symphonies that is way under the radar, but should be far better known are those by Ned Rorem