If the RCaudio responds correctly then you have a PPM transmitter. However, RCaudio is more promiscuous regarding the quality of the audio signal.
Your audio signal should look more or less like this:
And certainly not like this one:
If the signal is good then we know the cable & the transmitter are OK.
The next thing to suspect is the the routing of the audio signal. Make sure you can still see the signal on the oscilloscope when SPP is up and running. If you cannot then you must have selected an incorrect audio source.
Now, to some basic things that I might have started with:
1. Can you see the SPP version in the joystick window as seen in my previous message?
2. Do you use SPP for FMS or the generic version?
3. Can you see the 'Filters' menu in SPPconsole?
Accurate replies are a must.