I am not sure I understand. Single-connection ASIO cannot use a different rate for capture and different for playback - there is no direction parameter in ASIOSetSampleRate method. Also I/O buffer sizes are equal for both directions direction - method ASIOCreateBuffers has only a scalar parameter bufferSize for all non-interleaved channel buffers (which is logical since both directions use the same samplerate and the switchBuffer callback passes data for both directions - both directions must take the same time to fill up/consume up the samples).But it's probably easier if sampling frequencies are multiples and buffer size is chosen accordingly.