My eyebrows twitched a bit on the suggestion that the second splitter compensates for loss from the first splitter - you've still only got one signal being distributed, and anything lost at the first one is gone for good. It sounds too much like an audio version of perpetual motion. On the other hand, the two signals going into the sub are typically summed by the amp before undergoing amplification, so you are least are compensating for the second splitter - I'd have to dust off some rarely-used EE math to figure out how it all works out for sure. It certainly isn't going to hurt anything, at least.