So I just bought a T7500 with 48 gbs or ram (6*8gbs) that only came with 1 CPU, wanting two I bought the second riser that came with 24gbs or ram (6*4). After inserting the daughter board with the ram in the above configuration the second cpu and ram was not identified in BIOS and the secondary cpu fan ran at 100%. Assuming that the ram had something to do with it, I pulled all of the 4 gig sticks out and spread the 6 8gb sticks in dimms 1 2 3 for both cpus and that worked great.

In the below link the official dell position for this situation would be for the 4 gig sticks to go on the mainboard and the 8 gig sticks all go on the riser board.

64 | 4 4 4 4 4 4 | 8 8 8 8 8 8

https://www.dell.com/community/Desktops-General-Read-Only/Precision-T7500-Non-Supported-Memory-Configuration/td-p/3845298

My question for you all is, how does 4*6 + 8*6 = 64 gigs? (Should that equal 72 gigs?) There seems to be 8 gigs missing from the Dell documentation.