I wouldn't be so generalized. Balanced output of A90 is quieter than HPA4. So this needs to be case to case. And sure single ended output of A30pro/L30/A90 is much quieter than A90's balanced output.Didnt benchmark had an article, that balanced headphones out are technicaly worse than Single ended, because of the extra circuitry needed, which in turn produces more noise - although the XLR connection is superior in form of contacts? So this would be actually as good as it gets with all that power.
Also yes that A30pro is already as powerful as THX 789's balanced out but with single ended output.