I'm not much of a Congress tabbing pro, so if my suggestion doesn't work, hopefully someone with better Congress chops can weigh in.
For the top-6 - I think it should work the same way as speech. In Settings - Rules & Results - Congress Prelims, set "Truncate all IE ranks/recips to" 7. Does that not work for Congress?
At the moment, I think the only supported method for automatically advancing to Congress elims is to take the top X/chamber. If you wanted to do it differently, it shouldn't be too difficult using the Event Display to figure out the top cumulative speakers from all chambers and then manually pair the elim round with those entries.