It sounds to me like he is using a frog walker with a knee ascender in place of the upper ascender. My first system, and still the fastest I have used, was a straight frog walker, and I started SRT single up/double down; it changed my life, and that was how I climbed for more than a year.
You can still buy frog walker kits.
I will also never stop using Ddrt, and in any big prune, my stock setup is SRT with a 70ish' Ddrt system on my hip, ready to go. I'm so lazy that now, a lot of the time, I set the Ddrt line as my pull down line so that I don't have to carry it or pull it up. An upper ascender w/foot loop is still faster, for me, than a knee ascender, but I don't usually use it b/c the knee ascender is faster on and off rope, and it doesn't bother me to leave it on all the time.
This is how I bet he's using the system:
Maybe show him how easy it would be to use the same set up w/ a multicender:
Props to
@countryboypa31 for the videos. Derek is a beast.
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