question 1: have you read this?
http://www.harman.com/wp/pdf/multsubs.pdf
question 2: do you even have a pair of identical subs?
question 3: have you tried running them both and measuring the frequency response?
question 4: are you smarter than the techs at harman?
question 5: do you know exactly how grantc79 has everything setup?
"i'd bet a good sum of money" your answer to most these questions is 'no'.