The music has more weight and solidity to it
What you have done by placing the speakers further from side walls is to cut down on early reflections form the mid and treble - it allows your brain to process the primary signal before the reflections arrive - you hear more detail rather than a cluttered claustrophobic sound.
If you get the speakers away from the back wall (6 feet or so) and add bass traps you can extend the "solidity" into the lower midrange and bass (although you will lose some room bass boost). Bass frequencies below about 600 Hz go in all directions - so a speaker at two feet from the back wall will have reflected bass and lower mids being reflected back at the listener from the wall behind the speakers. It won't affect the soundstage as much as sidewall reflections of mid and treble sounds but you still lose a bit of solidity.