I used my K2 for wide Olivia when it first came out. I had no trouble with MFSK.
The K2 has a peculiarity, though, in that it can have a slight (less than 10Hz) frequency shift between filter settings. It always uses its wide filter for TX, so you need to use RIT, or engage the TX lock feature of your digimode program after clicking on the signal but before narrowing the filter. The Elecraft list has some discussion about sources for a fixed-level output board, which I bought and installed, with audio output connections made to the MIC jack. Leigh/WA5ZNU
