I wasn't realy speaking about things like bass quantity or clarity , rather sound character as a whole and it's flavor , it's " personality"
Mt220 reminds me of Sine, both have warm fluid silky smooth sound while being detailed and clean sounding, both have great dynamic and punch! Bold with authority yet refine and delicate... both could listen to for 8 hours straight and never fatigue ....
As for bass, mt220 don't have more bass in terms of driver tuning , mt220 is full size headphone, it's simply bigger, bigger cups bigger driver.
If sine was made as full size headphone as mt220 or mt220 as on-ear as Sine, they would have same amount of bass.
As driver tuning goes...
Now clarity I agree with you, Sine is more resolving and refine, that effortless sound Planars are known for, specially in bass area, mt220 has more thump to bass, Sine has more define better and more sofisticated layered bass that goes deeper... but quantity is about same...
I don't mean to say mt220 in the same league with Sine and could replace it, all thou for 150eu you get a lot of sound, and a taste of Sine character flavor.
People who are looking for closed back headphone and easy to drive, and want sound character of Sine without spending more then few hundred euro should definetly audition mt220!