Needs help on transcoding - I'm probably missing something

Hi!

I setup a Logitech Media Server (v7.7.2 - r33893) on Ubuntu 12.04 64bit, using a Raspberry Pi with Squeezelite as a player.
All works great.

Now I want to play a bit with the various transcoding options, which is one of the great features of the server software.
For example, I wanted to try resample to 44.1KHz some MP3 stream that are in 48KHz, and cause some stuttering on the Rasberry Pi.

So, I started with something like this in the custom-conver.conf:

And all works well. I see in the info output of Squeezelite that is receiving a PCM stream instead of an MP3 one, so the conversion is done.
Then I want to add sox in the mix to change the rate and output the final result in FLAC:

But this don't work. I see that Squeezelite receive a flac stream, but nothing is heard and the play stop after few instants.
I searched in the forums, look up the docs & the convert.conf file, tried some variations but I don't seems to get it working.

Any help?
Thanks!
Bye!