So, first of all, you would have to be or have someone in your party that is Level 7 to be able to get Bolster PL 8 (or Boon Access Bolster with 8 feat points).
Defensive Reflexes IX (18 feat points): 9 Advantage
Battlefield Retribution [formerly Battlefield Reflexes] (2 feat points)
Bolster PL 8: 3 Advantatge
Defensive III: 3 Advantage
Focus Action: 1 Advantage
That is 16 advantage.
Also, that chart you are referencing isn't accurate as it was using a roller that was found to have an error. I'm not sure if the chart has been updated since, but it is showing higher results on advantage than it should as I recall.
A ranged (Agility) character can have that exact same build, minus the two-weapon brute, and in its place take 2 more levels of Attack Specialization. The wouldn't gain the benefit of a Prone enemy, but could easily gain advantage from the enemy not knowing they are there.
In addition, an Extraordinary Attribute can gain the exact same build as the Ranged character above, and could get a WL 5 item to enhance them a few more Advantage to the attack similar to Deadly III.
And yes, you'll have lots of dice explosion happening, but that would be the point. 1-shot knock-outs are suppose to be a thing in OL, that is a key part to explosions and lower max HP.
The other part of Banes to consider is that you just have to beat the Defense on it.
For example, a PL 7 bane (that would be a CR 24 for a boon), just has to match whatever Defense score the target has, which would be anywhere from 13~24 in most cases.