Audio output on HDMI from an SX20
The HDMI output #1 contains stereo audio, which is exactly the same audio signal that is sent out on Line Out / 3.5mm stereo.  This is standard line out and contains the following audio signals:
          * Far end microphones
          * Local and far end program material (e.g. anything plugged into SX20 Line In, like PC audio)
You can use both HDMI audio and line out simultaneously, but you have to be careful about LCD monitors introducing delay into the audio.  See attached file "LCD monitors – audio delay – C Series".
The SX20 HDMI output is not a recording output, nor is the SX20 3.5mm line output a recording output.  Recording outputs need to have local microphones present as well as far end mics and program material.  Because it is not an integrator's codec, the SX20 (and the C20) does not support audio record outputs.  You need a C40 or better in order to have record outputs for audio.
HDMI output #2 does not contain audio signals.
Regarding volume controls – there is just one, which controls the overall level of HDMI and Line Out audio signals.  It is independent of RingTone volume, which is set in the web interface or on-screen menus, using the TRC5 remote.  There are no separate volume controls on the CT Touch for program material versus far-end microphones.  This is by design, to keep the user interface simple.  Any computer or tablet that is being used for Presentation material will have an independent volume control, which users are accustomed to, for adjusting the level of the program audio.
 
<strong style="line-height: 16px;">Microphone inputs on an SX20
The physical inputs are 3.5mm / 4-conductor.  The pinouts are listed in the attached doc "C20 and SX20 mic pinouts".
The audio signal is balanced mic level, at –35dB nominal.  This is slightly hotter than most 3rd party mics, so when using wireless mics, try Revolabs HD series which was certified for use with the C20.  Or use an appropriate mixer and adapter cable for other 3rd party mics. 
Although we provide 12V nominal for Phantom, do not depend on this to power 3rd party mics, as the spec is plus or minus one volt, which will fail to power some microphones.  Instead use an audio mixer to provide Phantom.
Keep in mind that the SX20 is a "Quick Set" device, not an integrator's codec.  It is very possible that Cisco TAC will not be able to support complex audio installations using 3rd party equipment.

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