I don't believe a mid is necessary in the X unless you really feel as though imaging is compromised w/o. I tested (in the stock speaker locations) the...

JLs: Just not as good as there subs and a bit muddy.

Boston Pro: EXCELLENT!!! Love them, just did not want to pay $550... though I am reconsidering. DDD and acoustic/unplugged recordings like Tracy Chapman, Nirvana, Lauren Hill, etc. sound INCREDIBLE.

MB QSD: Ahhhhhhhh (drooling) love the sound, especially jazz and vocals... but one grand is not in the budget right now.

MB Premium: the ones I run right now, good imaging, bright and clear. Not good at handing alot of bass so I run the amp crossover at 175 and send the rest to the JL 10" sub.

Focal Utopia: Loud and handle bass wonderfully but the sound is overly bright and a bit artificial.

Dynaudio and Morel: Speaker of the Gods... if you can afford them... GET THEM! I took them out of my X imediately after sampling them... I didn't want to fall in love and have to buy them.