Hi Bill,
Obviously it is no problem to tap off of the audio. And you can purchase a power divider (e.g. from Mini-circuits, like
this one) to properly split the coupler output. However, I think Stu nailed it when he noted that this will not work because of the inherent latency between the audio and the RF, which will be somewhere between 30 and 100mS, depending on your specific buffer and filter settings in PowerSDR.
If you are running AM, there is another way to accomplish this, though, and that is to use a detector to obtain demodulated audio from the radio output (input side of the amplifier). While I wouldn't recommend using a CleanRF brand sampler for anything, they do make a
detector that can be used for this approach.
However, all that said, if you are running PureSignal you don't really need to go to all the trouble. You can use the built-in PureSignal AmpView display to see exactly what your entire RF path is doing, linearity-wise. If you are pushing things too hard, the AmpView display will show you that immediately, as you will clearly see the gain curve flatten out towards the top. Just turn it down a bit, because PureSignal will fight you tooth and nail to make it linear, and the more you compress the external amp the harder PureSignal fights.
73!
Scott