exchange the 2.5 casings in the bottom of the R5 for two 3.5 casings? I have a couple of 3.5 drives I like to hook up.

Hi laloar57‌,

Maybe one 3.5 will fit if you remove the 2x2.5, but 2x3.5 wont fit. We do not support modifications, so, unfortunately there is not much more information on our part to help you with this. But you could also try posting this on the Notebook Review and Alienware Arena to see if other users have tried it.

I found in Ebay two aurora 5 3.5 hdd enclosures, that i think might fit in the bottom where the 2.5 enclosures are, they look they are the same width as the 2.5 one, not sure about the length. I do think the mod, would not let me add another video card, but i do not foresee adding more

video cards to it. I add the corresponding pictures.  What do you think they might do the job?

It appears that the 2.5 frames and caddy can be replaced with 3.5 frames and caddy.

Easiest way to tell would be to remove one of the 2.5 frames and then see if you can move the 3.5 frame

from the left and put in the bottom.  If they fit fine and or can swap positions I would say there is no reason why it wont work for 3 X  3.5 drives.

http://topics-cdn.dell.com/pdf/alienware-aurora-r5-desktop_Service%20Manual_en-us.pdf

Knowing that the Aurora R5 case only has room for one 3.5 HDD, and it came occupied with the model I bought, We decided to modify the bottom 2.5 HDD cases exchanging them for two 3.5 HDD cases.  

So we got two Aurora R5 3.5 HDD from eBay, and proceeded to take out the 2.5 HDD bay and installed the 3.5, as you can see in the pictures.

The Sata and power cables have to be 90 degrees endings or the case side door wont close.

The video card center stand had to be removed because it does not fit.

Waiting on the rest of the 90 degrees cables to come in to finalize the mod.

That is great, good job. Didn't see any drive cages on Ebay. Did your auction list a part number? Do you think a second video would not fit this setup? I have a 2TB laptop drive but I also have a 4TB external 3.5" I can take out and was hoping to add more storage.

Thanks. NEW Dell 13P1-4YN0G01 Alienware Aurora R5 3.5" Hard Drive Cage w 3.5" Caddy thats how I found the bay.    lonestar*tech512 on eBay , sold it to me.

Definitely if you go with this setup the second video card does not fit.

I had two 3.5 HDD from a previous computer that i just bought, the computer just died, so i have a lot on info i wanted transferred to the Aurora, and was not going to buy new 2.5 hdd.

Decided also not to add a second video card. 

The machine is stable, fast, and temperatures are ok.