Just an update on my inquiry a few days ago about a subtle midrange degradation in my 3.6s.
I should have done some troubleshooting before my comment on this forum. I completely broke down my whole system and cleaned all connections/contacts with "Kontak Audio" electrical contact cleaner including all cords/connections, tubes, fuses...etc. The Thiels sound as good as they have ever sounded. If you don't have any contact cleaner, the simple friction process of unplugging and plugging back connections creates a better contact.
I also did some microphone testing with REW software and my miniDSP UMIK-1 microphone with no major issues identified. Psychoacoustics tend to play tricks with my mind, so I can't definitely say the hard work needed to clean the connections or lack of work related stress over the past weekend contributed to the improvement.
Never underestimate the little things.