We were talking specifically about the 6th amendment. You seem to have changed the topic to just reliability in general, I'm assuming because you realize you are wrong?
In what way?
U.S. Constitution - Article 2 Section 4
Section 4
The President, Vice President and all civil Officers of the United States, shall be removed from Office on Impeachment for, and Conviction of, Treason, Bribery, or other high Crimes and Misdemeanors.
Article III Section II
"The judicial power shall extend to all cases, in law and equity, arising under this Constitution, the laws of the United States, and treaties made, or which shall be made, under their authority;--to all cases affecting ambassadors, other public ministers and consuls;--to all cases of admiralty and maritime jurisdiction;--to controversies to which the United States shall be a party;--to controversies between two or more states;--between a state and citizens of another state;--between citizens of different states;--between citizens of the same state claiming lands under grants of different states, and between a state, or the citizens thereof, and foreign states, citizens or subjects.
In all cases affecting ambassadors, other public ministers and consuls, and those in which a state shall be party, the Supreme Court shall have original jurisdiction. In all the other cases before mentioned, the Supreme Court shall have appellate jurisdiction, both as to law and fact, with such exceptions, and under such regulations as the Congress shall make.
The trial of all crimes, except in cases of impeachment, shall be by jury; and such trial shall be held in the state where the said crimes shall have been committed; but when not committed within any state, the trial shall be at such place or places as the Congress may by law have directed."
The process of impeachment is a criminal trial, therefore defendants in an impeachment case are criminal defendants, such defendants would gain the protection of 5th and 6th Amendment Constitutional Rights.
The 5th and 6th Amendments were passed after the original Constitutional text, and take precedence over the original Constitutional text covering the process of impeachment.
That means Congress must afford all defendants the same rights they would have for a Court trial including:
The right to a speedy and public trial
The right to confront and compel witnesses before Congress
The right to Counsel
The right to remain silent
The right to “due process”
The protection against being tried twice for the same crime