The just released Argon servo drive firmware version 2.1.0 adds support for encoders with analog Sin/Cos outputs. Drive allows selecting interpolation factors of 16, 64 and 256 for such encoder. This means that an sin/cos encoder with 1000 lines per revolution, would give resolution equivalent of 256*1000 lines. In addition to this, normal quadrature decoder 4x gain applies on top of that, meaning that 1000 line encoder will yield total resolution of 1024000 counts per revolution.
The FW upgrade contains also many other improvements based on the user feedback that we have received. For full list & download, see firmware page at wiki.