Steering wheel control (SWC) interface of BOSS Audio in-dash multimedia devices

[Romualds]

I'm considering upgrade audio system of my 2-nd gen Sienna and going to buy BOSS Audio Systems Elite BE9ACP.

I'm wandering if there is any information about steering wheel control interface of BOSS car audios? For Jensen devices there is the information that they has analog input and voltage levels needed for each particular command are documented in the user manual.

If BOSS devices also had analog input with different voltages I could develop interface board for translating voltage levels from steering wheel buttons of my Sienna to levels needed by BOSS device. I just don't want to spend more then $50 just for voltage level translator I can develop by myself.

Any information will be highly appreciated.