What happens when I use the 2 inputs of my svs sb3000 with Y rca
Nothing. It only raises I’m the input sensitivity. Max output will stay the same, but in normal ranges you might need to trim the gain back in the sub itself to keep the same level as using one input. Basically, it’s not worth the cost of the Y adapter.
For the old sub sale, he probably doesn’t know what he’s doing, or what to expect. Better placement, or integration should help. Or just turn it up!!!