The 6dB headroom thing is somewhat of a relic from the past and doesn't really apply if you stay 100% ITB. In digital you're all good as long as you stay under 0dBFS (with the caveat that certain analog emulation plugins likes to be run at very low levels)

I usually clip my master input by a couple of dB but it doesn't matter since my limiter take care of it at the final stage.