What is the biblical support for the original sin being an infinite sin? I have heard a few times recently things like "an infinite sin debt requires an infinite Savior".

What is the biblical basis for coming to the conclusion that Adam's sin was infinite?
I don't know if "infinite sin debt" has a more precise definition in some traditions, but as a concept, I'd say that the "infinite debt" alludes to the idea that the debt we owe because of sin is too large ever to be repaid.


  Hebrews 10:4 (NASB)
  For it is impossible for the blood of bulls and goats to take away sins.


The Hebrews writer says more about the idea in the entire chapter, but this is the thesis as far the question is concerned. Everyone has sinned (Ro 3:23). There is nothing we can do that will undo or make up for our sins (e.g. animal sacrifices, personal righteousness–Eph 2). In this sense, our sin (and the sin of Adam) could be thought of as infinite.

I don't think the saying you quoted is as much a precise statement of a specialized doctrine as much as it is a memorable, pithy statement in praise of Jesus.