I emailed Terratec a while ago, who told me they would "probably" develop GSIF2 drivers.
Now am I wrong or do you need GSIF2 for gigapulse and gigapiano 2?
You only need the GSIF2 (audio input part) if you want to run external audio into GigaPulse. You don't need it to run your samples through GigaPulse, or for the new GigaPiano - these only require the audio output part, which is defined by the original GSIF spec.
The other part of GSIF 2 is the MIDI input part. This gives no new features, but is intended to reduce MIDI input latency.