man , I dont wanna sound like the steroid advising duffus but , to get down to a true 6% bf ( hyrdostatic underwater measurements) some one would ether have to have a super fast metabolism. Or use say 25- 50 mcgs of t-3 with a low dose of test 200mg a week ,tren 75mg eod with winstrol 25mg eod to come in that low without losing much muscle.
I have read one a person gets down below 8% bf the catobolsim starts to take hold and eats up muscle pretty quick