Stock HU650 changed to Kenwood kmm-bt309, subwoofer suddenly quiet

So i just switched from the stock HU650 with an rca adapter in my 2007 Volvo S60 to a new kenwood kmm-bt309. This one got 3 pairs of RCA connectors for front, rear and subwoofer. Ive connected everything to the right connectors, ive tried to tune it as good as i can. However the subwoofer magically got really quiet after the stereo change.

With the HU650 the subwoofer was really loud, but now its barely noticable. the SW bass level is set to max (10) on the radio, the gain on the actual amplifier is also set to max. Should i enable bass boost on the stereo? Im seriously pretty stuck here since ive tried everything i can think of. The stock speaker amplifier works without issues with the RCA to DIN adapter.