What did he say?

Ive always heard to use -5 as well.

 

It's always been my understanding that -5db will give you a bit more buffer room from clipping than 0db.

 

That was my thinking

 

Actually, it's the opposite.

Think about it this way.. let's say for a moment that music has a single freq of 1KHz but that it varies in level from -15 to -5 db (the majority of the time likely down around -15 but hitting -5db during loud passages). If you set the gains using 1 KHz @ 0db you'll never clip but you also have power you paid for that's underutilized. Safe but inefficient. Now if you set the gains using -5db most of the time you'll not clip but you might during loud peaks. That's why some people, depending on the type of music listened to and how loud they typically play it, might even use -6db tones (or if really ballsy -10db).

Really, there is no specific tone and level that must be used. It's all pretty subjective and depends on what speakers you are setting the gains for (i.e. you wouldn't use 1KHz on subs or 40Hz on mids), the music source/type, how loud you listen to it, and what your level of acceptable risk is. Say you like to listen to EDM really, really loud...0db is what you should probably use. 1KHz at 0 or -5db are both good choices for our purpose.

Hopefully that makes sense.