Three points on bringing alcohol into the USA:

It's unlikely to be confiscated.
There's no limit on the quantity you're allowed in general, though there are sharp limits on certain types of alcohol that are considered dangerous (like absinthe) and on all products from designated countries (eg, Cuba). Unless you're bringing in items like these it's unlikely anything will be confiscated. Just declare what you bring.

You may have to pay tax.
The normal duty-free limit is 1L. Beyond that a tax applies, but charts at cbp.gov (Customs and Border Patrol) indicate it's small, on the order of $1-2 for hard liquor and less than that for wine and beer. Possibly because it's small, like Palal speculated, CBP seldom collects it. As a US citizen I've brought in 2-3L of alcohol on numerous occasions and have never been taxed.

You will have to check it in for your connecting flight.
You have to re-clear security when connecting from an international flight in the USA. The USA has low limits on the amount of liquid that can be carried in hand baggage. You'll almost certainly have to repack your liquor into your checked-in bags. That alone may discourage you from attempting to bring 6L of drink.