Alright folks, I'm back. I appreciate all the great advice immensely.
Last night, I took out the Cardas L-15 and swapped it for the Illuminations D60. Before doing this I listened one more time with the Cardas still in the chain to make sure I wasn't imagining things. Yep, it still sounded like I was listening through a thick plastic bag. The Cardas were hard to remove, but the D60s as always, slid right and stopped with a positive click. No matter what I connect the D60 to, it always has that same perfect fit.
I fired up the same Diana Krall CD I had just listened to a minute ago with the L-15 and...Voila!! Clear, beautiful piano and that lovely voice of hers! My system never sounded this good. The overall presentation was still sometimes just slightly tipped up, but maybe it's because I was playing the dang thing so loud. I spent a couple hours playing with isolation tweaks, and I ended up with a completely different
scheme. The DAC 1.1 sounded much more open without the BrightStar Little rock beneath it. I ended the evening with Black Diamond Racing #3 Cones and Pucks under the Theta, which settled the sound some without deadening it. In the past, the BDR #3 Cones have always over-deadened the sound of my source or amp, but not the Theta.
This morning I fired up the same CD just to make sure I wasn't dreaming. And yes, it was just as nice. So I thought, "the D60 did the trick!" Just to be sure, I swapped the L-15 back into the system, and guess what? It sounded good too. So what does this tell you? Where did all that heavy sonic fog come from? Improperly installed digital cable? Freshly fired up component not quite up to speed? Static build up in shipping?
I'm sure somewhere within all the ideas posted here lies the reason[s] for what I experienced. The Theta Pearl with the Bel Canto is very much to my liking. I can only surmise that the reason for my experience was operator error. Or could it be that plugging and unplugging the cables helped to discharge any static build up in the coax plug? After all, the previous owner had this unit just sitting around.
What do you folks think? And thanks again for your very helpful suggestions.