Is that the same Zapco as back in the day? I know companies like Soundstream were top notch and then bought out by another company and the name "Soundstream" stayed, but the quality didn't.
I have heard Diamond speakers and were awesome sounding. The shop I worked at sold Boston Acoustics Pro series subs, Soundstream (when they were good) among others and the Diamonds blew them away in terms of SQ. Bostons were too bright sounding. I still have a pair of Pro 5.4 Boston Acoustics that are sitting aound collecting dust. Too bad our cars don't use 5 1/4" drivers. It sure would make for more upgrade options.