The first configuration would be correct. The second wouldn't for 2 reasons, first  that the LARGER dimms must be in front of the smaller dimms. Secondly, you wouldn't have matched the 3 channels. Now a solution for that is to go to BIOS (F2) and set Memory Mode to Adv Ecc. You will lose 2 2gb dimms to make this configuration work.  Then place the dimms in the following config. A2, A3, B2, and B3 get 8gb and A5, A6, B5, and B6 get the 2gb dimms. Adv ECC mode drops the first channel, allowing to use 4 banks. The previous configurations we have discussed are for Optimized Mode. 
We're upgrading our RAM on our servers.  They all currently have 2gb DIMMS.  We have purchased 8 gb DIMMS.  How would be best add the 8 gb DIMMS to our servers to get the max memory?   For example, let's say there are currently 8, 2gb DIMMS and we want to add 2, 8 gb DIMMS.  What would be the best configuration for that? Thank you.
R610 RAM Configuration