Office of Grand Ayatollah Khamenei (may Allah grant him long life):
You should pay Khums dues to Wali Amr (guardian of the affairs of Muslims) or his authorized representative. Spending Khums for whatever purpose requires special permission.
Office of Grand Ayatollah Sistani (may Allah grant him long life):
You cannot pay religious dues to a person whose maintenance (nafaqa) is obligatory on you.
Office of Grand Ayatollah Saafi Gulpaigani (may Allah grant him long life):
One cannot give his Khums to people whose nafaqa (maintenance) is obligatory on him.
Office of Grand Ayatollah Makarem Shirazi (may Allah grant him long life):
You are allowed to spend one third of the Imam's portion (Sahme Imam) from your own religious dues for the said purpose albeit with observance of precaution; and send the rest to us so that it may be spent for the needs of Islamic seminaries and propagation of Islam in under-privileged and deprived regions.
Ayatollah Mahdi Hadavi Tehrani (may Allah grant him long life):
In this regard, you need to obtain a special permission from the Mujtahid whom you follow.