@whipsaw - they sound different because of the design and parts used.
Understand that power supply is where most of the sound comes from. If it can filter the noise of the AC, then you get a blacker background, faster transits, more detail, better control of soft to loud and loud to soft speed, etc. Transformers is where most of this begins. Then there are capacitors and resistors. Read up on Audio Note non-magnetic ones and understand why they sound different. Came goes for capacitors, Why would V-Cap, Dueland, Milflex all sound different, Ten you will begin to understand what makes sound.
Happy Listening.