@jovica Linear PCM is basically WAV, technically a WAV file has a short header on it that describes the format then its linear PCM data, you should be fine sending a wav to Lex as it will just ignore the header as a small glitch of data.
The important thing is that Lex needs the audio in 16bit 16Khz format but it looks like you hav that in the above format.
I'm pretty new to pythonista on ios but I've done a fair bit with Lex (and Alexa) in python for some code that submits audio to Lex using python & requests have a look at https://github.com/Nexmo/lex-connector/blob/master/server.py#L102-L109
Thats part of a larger application but should give you some pointers