Clear from the OP that second systems are not done out of dissatisfaction for the first, pace ebm.
If I start a second system, it would likely get its fuel from two different motives; first, I have extra gear that is not worth selling nor worth giving away. Example, I have some Adcom gear that sounds quite decent but is not worth much. It could form a nice second system.
Another motive might be to have a solid state system with different power and speakers which crave it OR a low power system with high efficiency speakers and a sweet low-watt tube amp.
If I start a second system, it would likely get its fuel from two different motives; first, I have extra gear that is not worth selling nor worth giving away. Example, I have some Adcom gear that sounds quite decent but is not worth much. It could form a nice second system.
Another motive might be to have a solid state system with different power and speakers which crave it OR a low power system with high efficiency speakers and a sweet low-watt tube amp.