Try changing out the tubes for lower gain ones. Instead of a 12ax7 try a 5751 or something similar.
Also keep your power cords as far away from the patch cables as possible.
And don't bunch the power cables up and tie them together. Try and keep them separated as much as possible.
Use high quality patch cables, such as Planet Waves, George L's, Mogami, etc.
Try sanding the paint off the rack rails to bare metal. This gives you a better ground.
Lastly Triaxis' are on the noisy side to begin with. There is a lot of hiss especially on Ld 1 Red and the Ld 2 Yellow and Red channels. A high quality lower gain tube will make a huge difference in not only noise, but overall "warmth" as well.