No control for subwoofer on Sony HU

Guys, brought one of the Vibe active optisound 8 underseat subs*. It's all connected up and working however I'm left feeling like it should be producing more bass. I've got a sony n4000bt with 2 sets of preouts. I've set the HU to Sub out but non of the sub controls on the head unit work. If I change the lpf it does nothing, if I change the sw gain on the HU it changes nothing! Anyone had anything similar and knows a fix? Thanks
*If anyone is looking at this it does NOT fit under an R52 seat!