memory question

Hi,

We have an Power edge R910 that currently have:

128 GB memmory:

8 X DUAL IN-LINE MEMORY MODULE, 16GB, 1600, 2RX4, 20D6F, BIC

we want to add 128 gb more memeory to the server

I have 2 question:

1. Currently we can only buy 8 gb DUAL Rank or 32 gb Quad Rank.

can we use any of above memories and mix it with our current memeory modules?

2. in whitch empty memory banks and in whitch order can we add the new memmories?

Thanks