Will,
You've got this wrong! I said that the MN21 runs at 6.8 volts. And the MN16 (M3T HOLA) also. And the MN11 (M3 HOLA). In other words, and of the "9 volt" HOLA lamps pretty much run at close to 6.8 volts. So, the P91 would be a 6.8 volts lamps as well, presumably.
Now, the 9 volt LOLA's, which would include the MN20, MN10, MN15, and N2, all run at HIGHER than 6.8 volts. Not sure what the exact voltage at good drive-level is, but it is noticeably HIGHER than the 9 volt HOLA's.
So, the LVR3I, set for 6.8 volts DC-equivalent, will UNDER-drive these lamps--whcih is perfectly safe, but less than stellar in terms of whiteness.
Clear?