Do you think the Zed minilith would be a good amp to power my SI 15 or should I keep my Concept CC-D1200. TheCC1200 has a few issues but has more power than the Zed but the Zed has a nicer build and can make more than the rated 600rms. But I like to have the overhead. Also the 15 has a slightly softer suspension, correct, than the 12? So having 1200rms on tap isn't needed. Who knows.

the ZED would be a good choice, the sub does not need much power to get rolling, maybe look at the XT-2000D,

but from a few reviews so far the ZEDs seem to be very nice

I only had about 350w on tap with my 15. The box was a little bigger than recommended(sealed) for a little more efficiency. It got loud enough for daily driving and was still incredibly accurate.

600 is more than enough, but it's always best to have more if you desire.

He called me a little earlier. I told him that 600 watts RMS is just fine but it really depends on how loud he wants it and how much headroom he wants. If it were me, I'd throw more than 600 on it if I bought a 15...although for 99% of my daily listening I'm probably not using any more than 300 watts a driver during the loud parts.