Classe DR25

I recently got a Classe Audio old model DR15 power amp
I would like to know for the right connection for the xlr input
cable:

1 pin = ground
2 pin = - negative
3 pin = + hot

or

1 pin = ground
2 pin = + hot
3 pin = - negative

Also would like to know if it safe to push for min 2-3ohm
loading speaker and does the dr25 sounding better than the later model
Classe twenty five?

Thanks!