Ok, an update...
I got through the change to epson water. I did exactly what you said and got him out into a small plastic cup with his old water. Filled his tank with new water that had 1tsp/gallon of epson dissolved in it, made sure it was at 80 degrees, and then floated his plastic cup in the main tank and every 10-15mins I swapped in a few tbsp of the epson water into the cup. I did this for about an hour and a half and then finally placed him into the tank. All things considering, he looked really good while in the cup. I think having such a short distance to go get air helped him rest a bit, and he looked pretty darn healthy in there. We tried to feed him while in the cup (flakes, pellet, pea), he wouldnt even consider it.
He's now in the new water with epson salt, and I have the tank only about half way filled; just high enough so that the heater can be in there, and the filter is running too, but MUCH shorter distance to go get air than this morning. He looks a bit dazed from it all and is laying at the bottom for the most part but, again all things considering, he looks really good! Unlike earlier when he had to swim a foot+ to get to the top, very frantic!, and then come crashing/sinking back down to get air, now he can swim to the top, grab a gulp, and then rest back at the bottom much more easily... he looks much less frazzled.
Something is still wrong, as he's still very lethargic, still looks very weak, and he won't eat a thing (it's been 4, going on 5, days now since he had any food).... but I am WAY more content with how things are now than I was earlier. And physically, he looks great!, color is good, eyes are good, he's breathing fine, etc.
I now know I've done everything I can, so we'll just have to sit back, keep our eye on him, and hope he gets better.
Thanks again for all the advice today, LBF, it really really helped!
I'll come back and post if, no, ONCE
he gets better.