Burger
I like the idea, just haven't been able to respond until now.
Why don't you average the number of critials hits based on the wheter it is DD, TD, or QD? Example if a 5AD - TD gets 15 hits, and the resulting damage die rolls 5 sixes, that would equal 2 critical hits, asuming rounding up. You could aslo round down if the result was 4- sixes to just 1 critical. Then treat the remaining sixes as regular hits, 1 damage and 1 crew.
I don't know how the math works out, but this would reduce the number of criticals, based on your system, but still have a good chance of getting them. It also might satisify everyones concerns about the total number of critical hits.
Just my 2-cents worth
Tom