Irig 2 amps and cabs - sounds boomy

Hey friends! Sorry if it was before, but i get lost in all ios bass threads - i have Iphone SE, irig 2 and Jazz Bass. While i keep amp and cab (svt pack) off - sound is like bells and growly. But if i turn amp on (even with all knobs flat) sounds appears to be too boomy. Like someone puts a piece of foam. What i'm doing wrong? I messed around with in/output levels, different headphenes - same... when amp and can are On - bass sounds too boomy, with mad lows