Line level surround input

I believe I'm missing something here. I'm looking around for audio receivers/Active 5.1 speakers that have line-level surround inputs to interface with a 5.1 sound card. I see very few that have this, Logitech Z906 and Areal systems. It looks like there are very few systems that will directly interface with the soundcard line-level surround outputs, why are they on there? Maybe the solution is to buy two sets of active speakers along with a single active speaker plus a subwoofer and use an RCA splitter from the center/subwoofer output? Are there any systems/interfaces/manufacturers I have not considered? This is just regarding the line-level surround outputs, I'm aware that s/pdif can do surround sound.