How to use an amp with a crossover

[TrollSelektor]

Ok so I have never built any type of home theater system before. Right now I am looking to get a basic 2.1 setup going. I think I know which parts I want but am not exactly sure how everything works. For instance, not really sure how to use this amp/crossover.
 
http://www.parts-express.com/pe/showdetl.cfm?partnumber=300-803
 
I am assuming that I would have 2 RCA jacks carrying all the data for my music plugged into the RCA inputs for L/R, I set the crossover to my desired level (probably 180Hz), then I would have a subwoofer hooked up via speaker wire to the high level outputs and play everything <180Hz, then I would have 2 RCA jacks coming from the RCA L/R low level outputs going into another amp (if I go with passive instead of powered bookshelf speakers) which would then go into the bookshelf speakers that will play everything >180 Hz
 
Also not the primary topic but what is the best way to get from line out into RCA? I am assuming I would just by an adapter such as this http://www.parts-express.com/pe/showdetl.cfm?Partnumber=240-137&utm_source=googleps.
 
Note: The reason I am using 3.5 line out is because my laptop is rather ****ty in the audio department- so I am using a FiioE7+L7 to achieve line-out from a USB connection. (I already have the Fiio E7 for my headphones)

 

[trog]

I am assuming you in the USA - consider Craiglist for used, cheap receivers with sub/LFE out?

 

[TrollSelektor]

Yeah I am, and I am searching but am not having much luck. BUT would that work? One of the major issues is am not 100% sure on how all the audio gear works
 
Edit: A lot of the receivers on there are still out of my budget or won't take line 3.5mm. Remember I already have the Fiio E7 so it costs like $10 to get the L7 to give it line-out 3.5mm

 

[trog]

Just feed receiver off L7 with a 3.5mm-to-RCA : almost all receivers would have rca red/white inputs ^^