well I like challenges, I would think this is possible ... depends on specs of course.
can you download and install the following software it will give us more details about your system
>> SPECCY <<
you can copy first page of details with a copy and paste of the screen will be fine for now
you may want to also then goto file and export details to a txt file we may need to reference to it later
okay the xw8800 can in many flavors, and we need some questions answered
1. Which xeon processor(s) you have?
2. your 6GB of ram how many slots are they using on your board (click in speccy under ram it will tell you)
3. what kind of budget do we have
you Realize a lot of these "upgrades" will be refurbished or used hardware, but that should not make you shy of it, I recently did a Q8300, and about to giveaway to a 12th grade kid to use as a home computer, and it runs great
Note: reference manual I found
https://www.manualslib.com/manual/667149/Hp-Xw8400.html?page=3#manual