Ok just got back from PetSmart. They gave me two free Tigers (one reg and one albino) after hearing most of my story, so I figured I'll give this one more shot.
First I tested their pH, and it is virtually identical to mine (7.0 on the money). I also bought a dip and spit, or sit and sh*t (whatever those hang over the tank containers are called), to acclimate the fish more thoroughly. Inside the the container I slowly mixed my tank water with the water in the container, in 10min intervals, which goes fine. The O's are actively investigating their environment in the container, and seem very content. Then when I fully transition them into the tank the fall right to the bottom, and lay at an angle. I've heard of them doing this to ambush unsuspecting prey, but it seemed a bit strange at this time.
Well during all this trial and error, my Bichirs have out grown the Oscars I've been trying to introduce, proportionally (especially with these two being the smallest O's I've got by far). So after my larger Bichir 6.5" swam straight to one of them, and coiled for a strike, I moved them into my community tank (20g), until they get a little size on them. In the community tank they seem fine. Happily exploring the entire space.
I also added a TopFin Power 60, since they were on sale today for $30, to supplement the filtration of the 55 until I can pick up a Ehiem. So I'll leave the tank to itself, until the O's double in size (read: prolly a month), and then try it again.
Thanks again for all the help. My Bichirs appear healthy as a couple thoroughbreds in Kentucky, so I really do think despite the size incompatibility issue today, all this has been a result of something that was on my skin affecting the O's, and not the Bichirs as air breathers. I'll post an update as soon as I have one, for any future searchers who may be experiencing similar issues.