I've never heard of a CPU being soldered into a motherboard of any kind aside from the atom chip set. I have heard of the GPU being soldered into the board. but that being a unit not a card. seeing as this computer is on the same line as the alienware computer set the card is a modular card. not a integrated chipset.
A simple google search for the system board or a replacement of the system board shows a stander socket for the CPU to set into with the standard Intel screw lock system. how ever the pictures are not of enough clarity to depict the number of video "card" slots.
In addition, I'm on the same page with you of upgrading RAM memory. once again the IT service manual suggests a maximum of 32GB's 1333 sodimm or 16gb's of 1600 sodimm ram via 4 sodimm slots.
In basic. I want an alienware without all the glamour that comes with one. I don't want the purple keyboards and what may have you. when this computer was offered to me in it's basic specs for free I thought why not make it top notch.
So I should only assume to get the best answers as to the abilities of the system board and it's slot counts I should contact Dell precision computer support themselves to get the concrete answers I am looking for. However I was hopping to cut out that step in hopes someone from dell or very well versed with dell was a member on here and could answer my questions.
If you feel that what I have said was wrong in any way about CPU's rarely being soldered into the system board please feel free to correct me. but it is my beliefs that a CPU is far too delicate to introduce to the heat soldering would intell. or with the risk of running a cold solder.