You know what you're doing it seems, but if you're planning on using the MH and A14 systems together look over the NTSB accident report (WPR09FA089). Though the probable cause of this incident was not pinned on any failure of the MH/A14 dual setup, they seem to have spent considerable effort looking into it in the 200 page document. Not trying to scare anyone, just that there's some practical things worth implementing from it. The pilot had previously set a state altitude record around 33K' and on this flight was above 38K' when something went wrong. He appeared to be a very experienced, but quite cautious, pilot.

The issue with the U2 pilots was that they were wearing uninflated suits in a cabin pressure way too low. Even 100% oxygen is insufficient at high-enough altitudes (The USAF has since increased their minimum cabin pressure). Caution is well-noted as several glider pilots suffered chronically after they repeatedly sought altitude records. Good reading is the recent Soaring Mag article on oxygen use.