I've been using an NHT SW3 passive sub for many years. Initially, it was powered by the companion SA3 amp with built in crossover, but the last year and a half I've had much better results using one channel of a Bryston 4B amp with a Paradigm X30 crossover instead.
In most cases the quality of the plate amps installed in powered subs is compromised because of size. Last year the manufacturer of a VERY highly regarded subwoofer told me the 1000 watt amp used in his sub couldn't come close to matching the quality of the Bryston I was using.
It seems that many of the class "D" or "G" amps used in powered subs these days need to have high wattages to compete against a well designed two channel AB amp. My guess is because a good outboard amp won't be restricted by size, it can use a larger transformer, better parts and will therefore be capable of superior current and better sound.
Having an outboard amp and crossover will probably end up occupying more space and costing more, so that needs to be taken into consideration.
Good luck!
In most cases the quality of the plate amps installed in powered subs is compromised because of size. Last year the manufacturer of a VERY highly regarded subwoofer told me the 1000 watt amp used in his sub couldn't come close to matching the quality of the Bryston I was using.
It seems that many of the class "D" or "G" amps used in powered subs these days need to have high wattages to compete against a well designed two channel AB amp. My guess is because a good outboard amp won't be restricted by size, it can use a larger transformer, better parts and will therefore be capable of superior current and better sound.
Having an outboard amp and crossover will probably end up occupying more space and costing more, so that needs to be taken into consideration.
Good luck!