Long story short - I'm sticking with the Eno having received it today. Already it's clearly "just right". The chaps at NA told me I'd hear a little more detail with the Muon, but that the sound signature would stay the same, so decided to draw this quite expensive odyssey to a close.
I think it's fair to say that the Eno is better than the ISOCAT7 (anyone want to buy a "pre-loved" one ;-) ). I might still see some benefit in putting the Sotm between my stock switch and the Eno. All opinions welcome.