The fluval is perfect...it should run in your sump and be moved to the QT when you are ready to hold something. Then cleaned out completely and returned to your sump when the QT is empty.
Along those lines, I have a 20G Qt and run Marine Pure balls in my Sump. When I have been setting up my QT I move 4 balls over and replace them with 4, and run an aquaclear HOB filter. Aside from my first time with it (where as you mentioned, I did have an ammonia issue), it's seemed to work quite well. Have I simply been lucky, or is there logic to my limited experience approach?
As for OP's question, I've had many similar thoughts regarding stress in QT procedures outweighing it's benefits. My view has come to be that it depends where the fish has come from. How long it was was and it's tank conditions. I actually just grabbed 2 yellow, and 3 hippo tangs from BigShow's place. They came from a 1.026 salinity tank, had been there for a fair bit of time, weren't treated with anything, and looked super healthy. I dripped them for temp acclimation, and in they went. Guess we will see in a few days. Alternatively, I bought a Naso from Big Als, and some Anthias before that, and they went right into QT for 3 weeks.