Can you confirm that nuevoplayer is the flashplayer included in AVS 2.1 distribution?
If so, how can I embed a rtmp stream using the config.xml file?
Thank you in advance!

I don't understand...
Can you see Nuevoplayer offered by AVS team on AVS website? No...
Even if we know each other (AVS and Nuevolab team), have good relation and respect each other,
we are 2 different companies.
Nuevolab is small one, that specializes in developing 3d party mods and products like Nuevoplayer.

We prepared special versions of Nuevoplayer for both: Clipshare and AVS scripts, so it's fully integrated with mentioned scripts, including extended, huge siteadmin integration.

RTMP streaming is always individual case of each user and is not default option for both: AVS player and Nuevoplayer (cannot be). RTMP protocol settings can be very different.
However in case of Nuevoplayer it's pretty simple to update player playlist php file (with xml header) to use rtmp server by Nuevoplayer.
It is described on Nuevoplayer's tips page: http://clipshare.nuevolab.com/tips
There was also thread by one of Nuevoplayer user:
rtmp-with-clipshare-and-neuvo-t83.html
There are several users of Nuevoplayer that streams using RTMP protocol... and Clipshare or AVS script.

Hope this helps..