Dude...that is epic. I just now checked this thread because I've been looking for something and haven't returned to read the comments lately. That soundtrack is awesome! That's one of my new reference tracks.
I've actually done quite a bit of experimenting with different metering and yea...to REALLY nail that lush low end, I have to rely on my sub and reference at the end of the day. The loudness metering can get you in the ballpark if you have a busy track and you already have a sub note to gauge the apparent loudness for the rest of the notes. That is where the Youlean comes in the most handy. I still have to use my trusty bx_meter to make sure I've got the sub balanced with the rest of the track.
Like you guys have said...ears. Though I just can't do it without a sub and a pair of DT880 Pro's. Lol. Those are actually my go-to headphones for getting sub levels in check. It seems nothing else, in that price category comes close.