We will add support for the new ETC variant of ethash (with reduced DAG size after epoch 390) in the stable version of 5.2, it is not included in 5.2a yet, but there is still at least three weeks before ETC reaches epoch 390.

  Download PhoenixMiner 5.2, add the command-line parameters -daglim 1 -dagrestart 1 (also may try -rxboost 1 for additional boost). The hashrate will be lower but that's unavoidable. It is also important to use auto-tune (do not specify -gt values) because the optimal -gt value may change with each new epoch, and will definitely be different than before. For maximum performance, you can try manually adjusting the -daglim value (the default -daglim 1 corresponds to 4006 MB DAG limit). Some cards will work with higher values like -daglim 4011.