ADS actually made an electronic crossover for the 1230/1530/2030, called the C2000 Biamp Control. As per an ADS bulletin, it can also be modified quite easily to work with the 1290/1590. I have owned several of them over the years, as I own a pair of 1530's and 1590's. The main difference I noticed in biamping was additional bass output, and not much else. I now use Velodyne 1500R subs with each pair, and find this preferable to the added expense of an extra amp and cabling. Occasionally a C2000 will appear here on the 'Gon and on Ebay. If you should consider this, and want to know how to make the mods to work with your speaker, I have the info on how to do it.
There is also an electronic crossover that Bryston makes that could also work quite well. It has adjustable crossover points and should match up well.
A real must-do, tho, is to make sure you use identical amps-it will make balancing everything a much easier task. I also tried a pair of PA-1's, and wasn't impressed at all with them. The bass wasn't that great, and power seemed to be limited if you like to play them loud.
And last of all, good luck! You have a great speaker!!!