I played with the snd_aloop module that Jaroslav added a couple of days ago. It just does what I wanted and seems to work ok :-) Thanks for this patch!
I would like however to expose this output as a PulseAudio profile. Using a string such as hw:%f conflicts with other analog output profiles, and the actual card index will vary depending on each hardware setup. Is there a way to have an alias or a configuration so that I could use a profile definition as aloop:%f in PulseAudio, and use arecord -Daloop for my monitoring app. By default the playback device would be 0 and the capture one 1. As long as the card index is handle automatically I am happy.
I tried to play with alsa-lib .conf files, no luck (I really have no idea how this works). Any ideas on how to add an alias? Thanks for your feedback -Pierre