They both look like great headsets and from my knowledge they are pretty solid against eachover.
Although i do believe the Tiamat has a better bass kick.
Also, the Tiamat is a 7.1 surround headset whilst the Chimaera is 5.1/
So the Tiamtat will have better audio and it will give more depth to the audio also.
Go for the Tiamats, i'm not sure on the prices though.