To get tracks loud when you’re going through the mastering chain you need to push into your AD convertor. It’s no good just pushing level through one piece of equipment for this you need to do some gain staging in small steps by just eking a little bit more level out of the compressor, a little bit more level out of your EQ, a little bit more level out of everything as you go through the chain.
You are only going to be able to push your AD to a certain point, without it breaking up. So like any other piece of equipment you need to learn how the AD sounds with the levels being pushed into it. Don’t concern yourself with the red light; because they all got a little bit a play in them, but some have got more than others. Different convertors will behave and react in different way to different genres of music. I have some that I could push miles over and they still couldn’t hear distortion.
Some AD’s have soft clips on them or soft limiters. I don’t really like these as they close the sound in too mach and it’s better to control this limiting with dedicated units.
You are never going to be able to get a track loud just by going into the AD; you are going to need some limiters after. SO I suggest using digital limiters after the AD to get the extra boost you require. I usually use a combination of two, depending on the track. I like the fabfilter, I also use the outboard L2 as it sounds better than the plugin. But depending on the track there are different ones for different styles.
I don’t have any scientific approach for level into your AD convertor, it’s just all feel and sound. It’s same with limiters, you can hear as soon as you start pushing the limits too high, because it starts pushing the track and closing the track in. you start losing all the really nice peaks, that you have put in with your EQ’s.