I have a Guild F512 12 string with a DTAR system in it. I've been fairly happy with it except it distorts and gets kind of compressed if I start to get aggressive on it. Would a K & K pure 12 string pickup be better suited for this guitar? Thanks
First which DTAR do you have and what year is the F512? Most all of the DTAR pickups were 18 volt to eliminate distortion when played hard that most 9 volt UST's encounter. You may just have a set of batteries that aren't at peak output so first try a new set and see if that solves the problem.
Next check your saddle and make sure it is coming in full contact with the UST sensor underneath the saddle. As Solid wood guitars shrink and expand including the saddle slot in the bridge there may have been a small separation of the two not allowing the signal to be true and pure or even a little buildup that just needs to be wiped clean.
On the DTAR Pickups that were used in the later New Hartford builds there is a Bass and Treble adjustment screw on the preamp itself that is attached internally to the endpin jack. If your batteries are fresh it may just be a simple turn of the screw to adjust down the output of whatever is causing the distortion.
These are just a few things to check out that may solve your issue without changing pickups. I have Jumbo Guild 12's and 6 strings with both the DTAR Multisorce and the K&K in them and they are both great pickups in their own right. I do have some feedback issues with the K&K mini from time to time but it has a nice tone to it. Personally I Like the overall tone and versatility of the DTAR Multisource because it will pick up the softest nuances playing softly and when operating properly I have never had any distortion playing hard.
Another pickup option you may consider that I have been dying to try is a Barbera Soloist. It is an actual passive saddle that has individual sensors in it under each string and from what I have heard they are crystal clear. If you google "Barbera Pickups" you will find their website.
Best of luck and I hope you get everything worked out with it whatever you decide!
TX