I have been an advocate of passive vertical biamping forever, because, speakers such as the Dunlavy line, easily show sonic differences between amplifiers, and to maintain coherence, it is the only way to go. Not to mention, the amplifiers maintain much better control in this configuration. I urge the OP, to seek out another exact Pass amp, and vertically biamp the Dunlavys, because it has been my experience, he has not heard what the Dunlavys are capable of. Understanding how difficult it would be to attain another Pass amp, it would be worth seeking out anyway, or, finding another pair of high quality stereo amps and vertically biamp. Of course, this could lead to another thread, as to finding a pair of amplifiers to replace the sonics of his Pass, but passive vertical biamping has been most impressive for me over the years. Just my final thoughts on the matter, understanding this thread has come to an end. Enjoy ! MrD.