Upgrading T7500 -- CPU

Hi everyone! Purchased a T7500 second hand! I installed a SATA drive and have plans to install an Sata 3 controller card and SSD in the future but for now, i have questions with regards to CPUs compatibilities and what I should belive/not believe.

I have read several spec sheets for the T7500. The first i read saying it only supports XENON 5500 series Processors (Duo and Quad) and I have read others indicating it supports XENON 5600 (Quad and Hexa Core) Processors?  which statement is true?? I have seen people on here and around the globe that have configurations with both types of XENONs in the T7500

I currently have a W5590 Quad Core CPU with 12GB Ram. I am looking to upgrade in the future (2nd riser card and whatnot) but not sure If i can mix and match. My theory is that I cannot use a 5500 and 5600 in the same configuration. It would have to be both 5500 series or both 5600 series

Is there a different motherboard? I have 0D881F MOBO currently. Does only this one exist for the t7500 or are there other versions which support the 5600. Have been trying to get help from DELL LIVE CHAT and they cannot give me a straight forward answer. After some time they were able to tell me that it did support SSD (thank the lord)

finally..looking at GPUs as well and obviously I need to figure out the configurations of my GPUs and CPUs to make sure compatibility exists. anyone have suggestions to which GPU since if I purchased a 3.0 it is backwards compatible :)

If anyone can clarify the CPU compatibility for me and any advice/suggestions for GPUs please let me know. 

I plan to install a Samsung EVO 850 250GB SSD drive when it goes back on sale (missed the deadline sale on NewEgg during BoxingDay :( ..price went up before I bought it, had it in my shopping cart and all)