Yes, ECS can run 31 KHz modes. But not as good as AGA. For ex, Multiscan mode is only 4 colors instead of (16 ? 256 ?) of AGA. I'm not sure about the bit depth of dblNTSC, dblPAL modes (I don't use them).
Actually you don't need full ECS. Just ECS denise will probably be fine. I'm not familiar with A2000 mobo revisions. You should check with a diagnostic tool (SysInfo) to see if you have ECS Denise.
