I think Sony classifies the SAVA line as Active Speakers, so they use a different device number (Sony 15, device 255) than other Home Theater systems.

Assign 31758 to AUX. Then test the following EFCs to see if your system responds.

Vol+ 32826
Vol - 31802
Mute 33594
Power toggle 32570

Here's how to test. With setup code 31758 assigned to AUX, tap AUX. Then, tap Setup (don't hold it) and enter the 5 digit EFC. When you enter the 5th digit, hold it and the remote will send the IR signal.

For example to test Vol +, tap Setup, Enter 32826. When you enter the 6, the remote will send Sony 15, device 255, function code 18.

If the tests work, you can semi-permanently assign these EFCs to buttons:
Tap AUX
1) Press Setup until 2 blinks
2) Enter 994 (two blinks)
3) Tap Setup
4) Enter the 5 digit EFC (e.g. 31802)
5) Tap the button to assign to (e.g. Vol-)
The remote should blink twice to indicate the entry was succesful.

The IR signals for a total of 48 functions (most of which are probably implemented in your speakers) are known. If the above codes work, I'll post the others.