Update computer

My system:Chillblast Fusion Valkyrie XB-70 Ultimate Flight Simulation PCCM Storm Stryker White Full Tower Gaming CaseIntel Core i7 3970X 6-cored Processor 3.5GHz (Overclocked to up to 4.8GHz)Corsair Hydro Series H100I Extreme Performance Liquid CPU CoolerArctic Silver 5 Thermal PasteCorsair Air Series Fans in Blue (complete case replacement pack)Asus Rampage IV Extreme Intel X79 Motherboard64GB Corsair PC3-12800 1600MHz DDR3 Memory (8 x 8GB sticks)Triple NVIDIA GTX Titan Black 6GB Graphics Cards in 3-way SU512GB Samsung 840 Pro Solid State Drive512GB Samsung 840 Pro Solid State Drive2000GB 7200RPM Hard Disk - 6GbpsBlu-Ray ReWriterBeQuiet DARK POWER PRO 10 1200W PSUCreative Sound Blaster Z Gaming Soundcard (OEM)TP-Link Powerline Ethernet Adaptor - turn your power sockets into a network switchWindows  10 / 64Elite Chillblast Cable ManagementWindows Optimisation ServiceExpress Four Day Build ServiceChillblast Software Assistance ServiceRazer Anansi MMO Keyboard and Naga MMO Mouse BundleCreative Labs Gigaworks T3 Ultimate Quality 2.1 SpeakersSennheiser PC 310 HeadsetEnhanced Instapak Internal PackagingEthernet PCI E RJ45 Card

The sytem I bought in 2013 new. So it has some years already. I fly P3d v4.5 without issues. The versions P3d v 5 and 6 plus MSFS 2020 I can not install due to a DirectX 12  issue which is not fully compatable with my video card.
Thinking to change one videocard in replacement for the 3 I´m havng at the moment (Not top class but middle) I do have an averidge framerate from 65 and I´m happy with that. So what could be a new card for me or not.
Second changing the mainboard with a faster processor but that would be to costly for me.
Hope I can receive some advice for the best solution for the DirectX 12 issue I´m having.
Thanks in advance
Jack de Heer