The volume problem is not with playing - it's with recording. You can see the same thing in Maemo Recorder if you set its format to PCM or WAV. The difference is that for PCM and WAV mode, Maemo Recorder uses the PCM inputs (dsppcmsrc), and for the iLBC more it uses the iLBC input (dspilbcsrc).

It looks like the iLBC input somehow corrects automatically for input volume in a way the PCM input does not.

Using iLBC is not an option for Seqretary Recorder since that format is not as easy to overwrite mid-stream as PCM is (with PCM you can choose an arbitrary location and just do it, iLBC requires framing).

When you use the headset (on an n810 at least), the recording volume is much better. This is something to be investigated.