D.A.S is a good company, but so is EV. Since you're already invested in the EV subs, You may as well get the same model tops. This will ensure a more seamless integration and you won't have to do as much messing around with settings to make them work the way they were intended.
That being said, I would go with the 12" EKX as opposed to the 15" model. You have a sub already, so using a 15" with a sub pretty much makes ANY low-end extension a 15" offers, useless or moot. I.E. the 12" will work just as well and you will save a couple of dollars. I have used the EKX line a couple of times and they work rather well. D.A.S is more popular in the European region, obviously, so if you are in the USA, you won't see too many of them. In 17 years of doing sound, I have only seen 1 D.A.S rig brought into a gig, I didn't get to hear it though. I too considered one of their higher lines but decided to go with RCF.
