Ben, note that the S710 isn't the current model most nearly a successor to the X2100. There's no specific replacement model, but a bit above the X1200 and below the X2200 would be the closest description. The order on the current models in descending order is X2200-X1200-S910-S710. So, the S710 can be considered(except for the added Atmos capability for two rather than four overheads)to be between two and three steps down from the X2100.
If Atmos processing isn't essential I'd strongly suggest the X2100 over the S710. It has the higher grade Audyssey MultEQ XT, and my view is that you should get the highest version which is within your budget. If Atmos is necessary, consider the
X2200 .
