The EQ 1 should be fine. I've never used one before, but it looks like it's basically an outboard Audyssey sub EQ. I've compared SubEQ, antimode dual core 2.0, and mini-DSP. For user interface, antimode is probably the easiest to use, but has a hard time driving a pro-amp. MiniDSP works like a charm, but only has 6 corrective slopes and needs a mic/computer/REW. I'm sure the SVS would be fine, no reason for it to not be. Basically as long as it can apply a 12db/oct boost starting at the in room roll off point and also do some room correction you'll be fine. I only skimmed the manual, but it seems like it should do this. You'll also want to implement a high pass filter if it can do that at around 10-20hz if you plan on pushing the volume up.
The extra unit isn't for crossover, but for the stuff mentioned above. I don't know if that was unclear or not. Which room are you putting this in and what are your plans for this? Are you going with two to create a smoother in room response? If you have a master carpenter you may also want to consider a more custom box and simply mimicking the design of the flat pack.