Elite velours are fine but i would not waste money. Stock pads are superior and intended sound end of the day. I would switch the pads depends on my mood. Switching is very easy. Balanced is more fun, stimulating but fatiguing, analytical overall better.
A20 amp is waste of money. Good options are:
magni 3+
magni heresy
asgard 3
magnius
jds atom
topping l30
thx 789
thx 887
DAC:
modi 3
atom dac
topping e30
modius
Expensive ones most likely will not sound better. Since you can't use balanced with 1990 i recommend E30+L30. Class A single ended Asgard 3 amp might work nice with DT 1990 as well. Since you are considering $400 A20 i think modius+asgard 3 dac+amp stack for $400 would be nice for you.
A20 amp is waste of money. Good options are:
magni 3+
magni heresy
asgard 3
magnius
jds atom
topping l30
thx 789
thx 887
DAC:
modi 3
atom dac
topping e30
modius
Expensive ones most likely will not sound better. Since you can't use balanced with 1990 i recommend E30+L30. Class A single ended Asgard 3 amp might work nice with DT 1990 as well. Since you are considering $400 A20 i think modius+asgard 3 dac+amp stack for $400 would be nice for you.