hsk, to help answer your question about the double poon kiu:
a poon kiu is a circular block, and there are a few variations of it in the LKH line (I’m a 7th generation student, grandmaster is my si-gung)
A) Dahn poon kiu - this is the inside to outside circular block often seen when we execute sow choys, i.e. left hand circles clockwise as we shift from right to left gong ma and throw the right sow choy. The left hand executes the dahn, or single, poon kiu.
B) Seurng (double) poon kiu(a) - this is the technique that I think fu pow is referring to. The most common place we see this technique is in the following sequence - usually something like diu ma (cat stance) chin la-seurng poon kiu - sei ping ma chop choy (or fujow, or chin ji choy, or chang jeurng, or whatever). In this technique, the left hand drops downwards, palm up, all the way around into a grab or a cum jeurng at the end. In mid-rotation, the right hand flips forward and performs its own circle, ending above the shoulder, where you can follow up with a yum chop choy. The first block is actually the right hand making contact with the forearm, followed by the left hand’s grab or cum jeurng. Two circles –> Double poon kiu.
C) Seurng poon kiu (b) - a variant on the double poon kiu, seen before the chang fu knee kick techniques and sow geuk sweeps, as well as sow choys. Unlike variation (a), this one is better done in a more square stance rather than a cat stance, although (a) can work in a stance other than a cat stance as well. This one starts basically the same as variation (a) but is more east-west. Again, the left hand drops and then the right hand performs it’s forward circle. This time, however, the left hand follows a wider path - it shoots all the way to the left as you step towards the left, then circles clockwise inside to out, as in the dahn poon kiu, effectively “sticking” the opponents strike, then sweeps it back outside, opening the opponent up for the sow choy following up.
Hopefully that made sense - It’s probably way easier to show than type!
Fu-pow, Sisuk, or anyone else, please make any corrections if you see something stupid 
GL