C1 mk1 is a marvelous speaker. Also, IMO the mk2 version does not improves significantly upon the mk1 model (if at all). Certainly not to justify the large price difference between the two models, i.e. almost a factor of two.Paul there is a difference. I upgraded from the original C1 (7000 USD) to the C1 Signatures (8500 USD) not the MKII (7500 USD). Granted with the Signatures you pay for the finish and 10 yr warranty. That being said the MKII/Signature is less nasally sounding than the originals. I NEVER thought the originals sounded nasally until I heard the 2 side by side. Also the MKII sounds better at lower volumes. More efficient?? I'm sure a lot has to do with the upstream components (source cables amp etc) too. If there is a downside (excluding cost) it may be the MKII/Signature might not play as loud. That observation is from memory. When I had the 2 side by side I did not push them at all. It wasn't until several weeks later I finally pushed the Signatures (I don't have a db meter to prove it) but again from memory. So for me since 99.8% of my listening is lower levels the Signatures work out much better for me. Don't get me wrong the original C1's are world class speakers.
For whatever it is worth my system is
Meridian G08
Nordost Frey ic and sc
Octave V70SE tube integrated