Well, to conclude (maybe) this thread, I have spent a further couple of weeks swapping phones (650's and 701's) around between the Caiman phones output and the Slee phones output and have detected differences, but none which lead me to say one is better than the other...which basically means the Caiman phones output is a good as a £450 Slee Solo as far as I can tell. So (as most of you know already) the Caiman DAC/headphone amp/pre-amp is, in my opinion, an out-and-out bargain.
Phil