Hi Bob,
My first impressions of the IB1S's has not changed and I have owned a pair for 2-3years now. I have not heard a more natural sounding speaker. As has been mentioned already they have an amazing 'shut your eyes and you're there' capability.
When used for mastering it has become a journey of discovery that has ended in the solid realisation that any problems are NOT the fault of the speaker. With some room working and re-positioning I now have a much better setup for critical work. I will re-itirate what the previous poster mentioned about the top end though. Without thought to this the IB1's can give the impression of being bright. I dont believe that they are bright but simply a bit more pernickity in terms of setup than some monitors to get the top end sounding correct.
When auditioning amps I found an old Mark Levinson amp (no.331) that literally blew away the new Bryston 4bb with these speakers. Highly recommended. A friend has the 333 and I imagine bi-amping with a pair of these would be sublime.
Something else that must be mentioned is that they are totally non-fatigueing to work with for long hours and are always a pleasure to listen to music on.
Something that might also be relevent to you is that they co-exist very nicely with the Sennheiser HD600's when referencing to cans and back. Always nice to have some continuity
