What do you mean with 'drive baseboard' ?
If you are concerned about your RAID card having only four SAS/SATA links, please consider that either the RAID card provide multilane SAS (1 connector carries 2/4 SAS links) or the server disk backplane integrate a SAS expander to provide more (in your case, six) downstream ports.
In other words, you should have no problem installing your new drives.
UPDATE: ok, so you have a backplane limited to only 4 SAS units. You need to replace your backplane with something similar to that, but to be really sure you should contact DELL support. Fortunately, the W814D (6x SAS) seems quite cheap on Ebay so you can always try and see what happens.
Regarding the drive question (rightfully) raised by @gh0st: with a PERC H200/H700, equipped with modern (release date > 2013) firmware release, you can use whatever drive you want (both SAS and SATA).