Anyone with passive subwoofer/s with external amplification?

@highend64  I have more faith in the specs of that Crest CA9 than the Velodyne branded amp, so I would say you did well there. The CA9 is a pro-audio amp, so you just might want to verify that its internal input sensitivity jumpers remain set to the default 0.775V for home audio use (see the manual).

I have a pair of Cerwin Vega CLS-15S (15" ported) subwoofers and one of the plate amps failed (cheap power supply caps). I converted both to passive, powered by a Crown XLS-2502 amp, which features an internal DSP with adjustable 24 dB/octave low pass filter. My floorstanders have the same usable response as the subs (25Hz), so I didn’t need a separate sub controller/EQ and was able to use the same digital PEQ profile for everything. This was definitely a step up in performance and reliability from inexpensive plate amps.

@ted_b The jumpers are set to default sensitivity with is ok. The SP-8000 has a fixed LPF slope at 18db/oct which I think is more then ideal but honestly prefer the 24db slope. The Crest is very rugged for sub use but like you mention, it is a pro amp. Also do the the fact it is a pro amp, fan noise is another issue even though it is pretty quiet, they can be heard in a small room with low passage or low level. Normally I dont listen low but I dont listen too loud either so the threshold of listening to the fans is masked. 

During that time of development both Atlantic Technologies and Velodyne offer misleading subwoofer room placement suggestions.

From the 2006 Velodyne SC-1250 manual: "Remember that the built-in 7 band EQ will help to get the most performance out of your subwoofer no matter where it is placed."

I was taught what is now referred to as the 'subwoofer crawl' sans the crawling, in the mid 60's by a recording engineer. Even today the home audio manufactures are still suggesting generalized placement or the time and energy consuming trial and error placement suggestions. EVERY room is unique and the crawl need only be done once to map your rooms multipal standing wave bass modes to position your subwoofers within. There are a number of other low frequency advantages for using these room locations.

Not long after Velodyne developed their Digital Drive Series they learned the requirement of locating the rooms modes as the first step after unboxing.

Regardless, using the AT or the Velodyne it will take far less gain and EQ if the subs are positioned with the rooms bass modes. While there's no free lunch with -3dB subwoofers you get everything from the recordings compared to -6dB rated woofers. 

I believe the AT SP-8000 requires playing a low frequency source using a sound pressure meter or a real time analyzer to (individually?) set its parametric EQ's. The Velodyne SC-1250 will preform its Auto EQ using its internal Sweep Tones, the supplied mic and the touch of the remote control to adjust seven frequency bands from 20Hz to 150Hz within 1Hz increments to all its four presets. The SC-1500 offers a few more parameters that are adjusted during Auto EQ. All the best.