Combo Amp Piggy Backed On Closed Back Cab Speaker Question

I'm putting together a new live rig composed of a Marshall 6101 30th Anni combo sitting on a 2x12 closed back cab with diagonal speakers so it look slike a mini 4x12.  The cab is now loaded with a pair of ET65's and it sounds exactly how I wanted it.  I've always used G12-65 loaded Marshalls and the WGS speakers put a serious smile on my face.  I need a new speaker for the combo.  Having the combo on top of the cab let's me hear what's going on without having to crank the cab but the stock 200w EV is a lazer beam and way more sensitive than the ET65's so much louder.  I tried a G12K-85 but it was still too loud and bright.  I can easily put another ET65 into the combo since I usually run it at 50w when I run it alone but being opened back I know the speaker will not have the same lows and will be brighter.  I've been wondering if a "darker" speaker with comparable sensitivity would be the way to go and then the question would be which speaker?  Option two is to just run another ET65 in the combo and maybe port the cabinet to even out the low end between the two.  Your thoughts and comments are much appreciated.