You won't find any new board that will take either of those CPUs -- which were current a decade ago.  Anything you find that will take either CPU will be that age.  And given that, give serious consideration to either building or buying either a completely new system -- or at least one a minimum of 7-8 years newer than that one. Just about everything in that system is completely obsolete -- start over with something newer.  
I had my Dell XPS 9000 running well until one day I had to restart my pc and I got stuck in the bios loading screen, stuck halfway and doesn't progress further. I can't get into the bios menu or access anything. I have tried everything from forums to forums. changing CMOS battery to trying 1 memory stick etc. I have came to a conclusion that my motherboard has gone dead. It beeps 5 times which is the RTC issue but I changed CMOS battery and didn't fix the issue. Anyway I'm planning to buy a new replacement motherboard and deciding to do some minimal upgrades. Maybe changing to a Xeon X5690 but I'm not sure if it would just plug and play. Also planning to replace the PSU with an EVGA 650w and maybe some ram recommendation would be appreciated. Thank you for you time for reading this far!My Specs: i7 975 Extreme Edition12GB DDR3 ram (mobo had issue and only detected 8GB)GT 1030 2GB OC MSI Do let me know if you need any other information.   -jochu 
Dell XPS 9000/435T Issue and Upgrade