You are correct, most of the receivers with two jacks are no different than using a y adapter as it is the same signal. Some of the higher end receivers coming out with the latest setup calibration offerings, are now incorporating 2 or more seperate subwoofer channels.

M80s VP180 4xM22ow 4xM3ic EP600 2xEP350
AnthemAVM60 Outlaw7700 EmoA500 Epson5040UB FluanceRT85