Hmm... from what I understand the pre-bleach is used because the formaldehyde in the stabilizer was switched out due to exposure control regs. Hence stablizer became 'final rinse' (photo-flo and miconazole).

I believe the pre-bleach now contains some chemistry that generates the formaldehyde 'in-situ' and thus is needed for maximum longevity of the resulting chrome.

I guess I'll be corrected if wrong!