Most subs have built-in crossovers in the plate amp. most will have low pass (I think that's right) for the sub. some like the adire shiva se will have a plate amp (hypex hs200 I believe) with a high pass for the mains, if you want to roll them off and prevent bass from going to the mains. most don't have a high pass or simply don't want to use one and run the mains full range. it just depends on which is the worse of two evils. I prefer to run mine full range and just use the sub for the bottom octave.
most will hook up the sub using secondary pre-outs from their audiophile 2CH preamp or integrated amp and a long pair of interconnects. some don't have secondary pre-outs and instead use high level (speaker level) inputs to the sub, like the vandersteen sub does.
most will hook up the sub using secondary pre-outs from their audiophile 2CH preamp or integrated amp and a long pair of interconnects. some don't have secondary pre-outs and instead use high level (speaker level) inputs to the sub, like the vandersteen sub does.