I lean toward Preta Path. Hiruzen described Onmyōden as a combination of all 5 Elements, which Preta Path absorbs... But I wouldn't be surprised if that wasn't the case.
That wasen't the Truth seeking orbs that was just fused elements. If it was the Truth seekings orbs Hiruzen wouldn't have regenerated similar to Minato.
I lean toward Preta Path. Hiruzen described Onmyōden as a combination of all 5 Elements, which Preta Path absorbs... But I wouldn't be surprised if that wasn't the case.