As everyone said, the Y-splitter thing works just fine. I think I bought mine at Radio Shack.
But when I did mine, I got this weird low hum when the subs were hooked up at the same time. If I unhooked one, the hum went away. I guess I was getting some kind of feedback or interference. I couldn't make it go away, until I happened to touch the metal parts of the 2 sub cables together. Voila! No more hum. How weird is that? So I ended up zip tying the cables together to get rid of the hum.
Anyone else ever have this happen?