A sensitivity of 90dB is above average and rather good. Above 90dB is excellent.
I doubt that the original cabinet speaker was playing louder.
Of course you’ll get it louder with PinWoofer or a DIY amp solution. But I wouldn’t expect too much true “Boom” with the current setup in this machine (of course that is also a matter of perspective).
It will result in a quite dominant mid-high bass dominating the mix without any depth or sub bass. Some people like that, but it’ll sound quite unnatural.
A true and integrated “Boom” would require a bit more work like balancing the subbass (EQ), matching the signal to the back box and playing position (SPL mic or better REW and a calibrated mic), a bigger woofer or even array of woofers.