I use Dyn as well. I had them fore and aft but I ended up removing the rear speakers because their placement is just really bad. I even went through the trouble of sealing the rear area of the speaker and aiming them with rings. I think the main problem is that the speaker is fairly separated from the panel and grill, so it gets a hollow wonky sound. They are also much to close to your head so its impossible to get any imaging potential out of them. The time delay feature in the deck did help, but it was just never good.
I just use the fronts now powered by xtant monoblocks. I previously used JL to power my fronts and still use a JL 1000.1 to power the sub, but I was never happy with the JL's on the dynaudio's - too bright and tight sounding. I would strongly suggest changing amplification. Look at these:
http://www.xtant.com/html/products/xtant1.1i.cfm
I know it only says 100watts, but it is a high current class D amp and delivers more than enough power for the Dynaudios, so its hard to compare to normal a/b amps. If you know Dynaudio, you know they need a lot of power.
Its probably not what you want to hear, but if you really need to use rears, I would nix the stock placement and build some sort of pod in the far rear of the car - maybe integrate them into the cubbie holes somehow - or maybe you can buy premade boxes and bolt them in place using the rear cargo net bolts.
I bought mbquart for a long time before finding dynaudio. I also owned Diamond Audio and in fact use a DA sub and it matches well with the soft Dynaudios. I would stay away from the tinny, overpriced mbquarts and look for a diamond audio dealer. Diamonds (HEX) mid to high end levels would mate very well. But I have ot ask, why not use Dynaudio back there and then you know they'll match?
Do you have a sub yet? Stay away from Dynaudio's car audio subs, they are really slow, weak and require a lot of airspace, blah! MB quart 12" subs arent bad actually...
Good luck, let us know what you decide to do.