I've used a handful of successful arrangements for speakers like these. The eight π loudspeaker uses an Alpha 10 on a midhorn and reflex-tuned rear chamber for the bass. I use a PSD2002 with 1.6kHz crossover. The one π, two π and two π tower speakers use a smaller tweeter crossed over higher. For many years, I used the KSN1038 piezo tweeter and I could count on very good performance from that part. But it looks like I'll be switching to the Vifa DX25 soon because the KSN1038 has been discontinued.

The KSN1038 is a compression horn driven by a small cone diaphragm. Performance is good particularly for the money. But supplies are nearly exhausted, and I'm not sure if and when CTS will find a buyer for the tooling. So I've redesigned to use a Vifa DX25 dome tweeter, which is silky and smooth. They're more expnsive, but they do sound nice.

I considered using the APT tweeters when making the change, but I decided on the Vifa DX25 instead. I used a first-order filter on the Vifa, and I suppose that might work on the APT too. But unless a person is very careful with input power, I'm not a fan of first-order crossovers on compression drivers. It's too easy to over-drive them and send the diaphragm into the phase plug.