I've been VERY impressed with the sound in my '13, but I haven't been able to determine which system is installed. The original window sticker doesn't indicate Premium sound, which led me to believe no subs. I haven't noticed a separate sub adjustment on the equalizer, so I'm assuming they aren't installed, yet this car has crazy bass..which I love! Did we just luck out and get great sound with the standard system? Is there a simple way for me to determine whether there are subs, without removing seat backs?.