I understand your point in terms of medication and dosage. While I was able to eradicate E Histolytica, it was from a much stronger dosage than that of what Dr. Cahill prescribed.
However, I believe Jazzy and myself have advocated numerous times that Dr. Cahill is best for providing an actual diagnosis. For me, Dr. Cahill was the only lab/Dr. that was able to diagnose my problem. Has any other lab came back with Giardia for you?
Cryptic Giardia is a tough one and as Shrimpy has said, Dr. Martin Wolfe at GW is an expert on the matter.
I'd recommend doing Metronidazole and Quinacrine together. You'll need to get quinacrine from a compounded pharmacy. If you have issues getting it, send me a private message and I can help out.