You could certainly use an APT tweeter, and it would probably make a pretty good speaker. There are three things that make the Motorola KSN-1038 an attractive component - It performs well, it's inexpensive, and the implementation is simple. But much of this could probably be said of the Eminence APT tweeter too.I suggest using the PXBII3K5 crossover and an attenuator on the tweeter circuit much like the cable assemblies used on the larger models of π Speakers having compression tweeters. You'll probably not need the bypass capacitor C1 for top octave compensation, but I'd still recommend analysis with Spice to ensure that the tweeter crossover filter isn't peaking or overdamped. You'll also want a Zobel on the woofer in this configuration and for the same reason.