Is it possible to add your BPN-SAS2-H6IR to our existing twin server called 6026TT-HDTRF, to have SAS2 support, we already have 2 add-on cards per node so we can't add a 3th additional SAS2 controller?
No, that is not possible, your server uses X8DTT-HF+ mainboard, you need X8DTT-HEF+, because this board has an additional PCI-E 2.0 x8 slot to supports SMCI SAS daughter card ( BPN-SAS2-H6IR).
Also this solution is only available on 2U twin(2 nodes) and with 2.5" hdd's server called 2026TT-H6RF
http://www.supermicro.com/products/system/2U/2026/SYS-2026TT-H6RF.cfm