The OP idea is to stick as far as possible to fitting everything into the case of an unmolested compact. I would sacrifice expandability and power to stick with that plan.
BTW, after measuring up, there's no way in heck an 840AV logic is going to fit in either an SE or CC case, even with a sub-basement. The best, expandable, 040 board that will fit in there is the 630/640 series.