Many thanks to you both for your help and advice.
I can't see anything wrong in my audio setup - not to say there is nothing wrong but I can't see anything!
Been thinking about it and have come to the decision that I'm probably just going to give up with the Sonuus i2M.
I bought it two years ago as, not being a keyboard player, I intended to use it to compose melody lines using my most familiar instrument, bass, for inputting my ideas into PT in MIDI. It has never been a success and I decided the other day that it either has to become useful or go. It just doesn't track accurately and can I spend more time cleaning up the MIDI, deleting spurious notes and correcting wrongly interpreted ones, octave jumps etc., than doing in several attempts with the MIDI keyboard.
It also can be used as an audio input but when I tried that I met with the problem I mentioned here. The bottom line here is that I have my Alesis USB Multimix which works extremely well so can live without the i2M as an audio interface.
In fairness to Sonuus they have tried to help as much as they can and are currently looking at a couple of sample files to try and explain the tracking problems but for me it just does not work in the way that it's portrayed in all the promotional and demo videos - its been a huge disappointment.
Thanks again for your usual prompt response but on balance I don't think it's worth taking up any more of your time with it.