Clarify requirements around headphone levels about ohis HOT 1 OPEN

I'll just add a few explanations about where things become hard to follow:
The standard does not specify impedance requirements. It states that speaker impedances can be between 8 and 64 Ohms but also that it can sometimes be as high as 300 Ohms, without specifying an upper limit. However, the standard does specify that the full volume amplitude must be between 0 dBV and -10 dBV. Thus an implementation would have to keep this amplitude at all impedances.

What is needed is to specify a range of impedances for which the device must respect specific amplitude levels. With an added note that any impedance outside of those ranges might work but with no guarantee.

The last problem is that, if using a resistor to do a divider bridge, then the full volume amplitudes won't be respected. Indeed, if we take the numbers specified in the current version of the specifications, there is a ratio of >37 between 8 ohms and 300 ohms, but a ratio slightly above 3. Thus, it is very difficult to follow the standard if the implementation is using a divider bridge (the driving voltage would need to be very large with a very very large impedance before the OHIS connector.

from ohis.