SpEd, I'm sorry for being so short on my original answer. Your issue seems to be about your main tank having ick in it. Gonna have to keep ANY fish out of it for 6-8 weeks and let it die off. Otherwise, QTing new fish will do nothing to solve the problem you have now. QTing new fish will only help you avoid any new ick issue AFTER the main tanks problems are over.
The remaining fish. How long have they been in the main since the others died of ick in the past? Have they been ick free since the others died?
"Life may not be the party we hoped for but while we are here we might as well dance!"