I agree with Evan. There has been much discussion that reading relative voltage at the audio stage is somehow not a true "S" meter, but the standard is based on 50uv at the antenna terminals for S9 and I know of no commercial rig that measures that directly. All measure an equivalent later in the amplification chain and usually not at the original RF frequency, so measuring toward the end at audio levels is just as valid. I am more bothered by radios where the S-reading varies with whether the preamp is on or off...the signal at the antenna terminals doesn't change with the preamp control, so the S-meter reading shouldn't either.
=Vic=
Vic WA4THR