[Icecast] Streaming 2 different sources with darkice

[Joel Ebel]

I'm looking for ideas here.  This probably will wind up being more of an 
alsa problem, but I thought the people on this list might have been in 
similar circumstances and have ideas for me.

I work at a radio station with both a webcast and FM broadcast.  We want 
to use icecast both for our webcast and as a backup studio to 
transmitter link.  However, the webcast audio needs to be 
post-processed, but the STL needs to be pre-processed because the 
processing gets done at the transmitter.  Our solution to this was to 
get an in-studio AGC to use just for the webcast.  So now we've got two 
different audio streams we need to send to icecast.  We've got an 
M-Audio Delta 66 with the post-processed audio on lines 1 and 2, and the 
pre-processed audio on lines 3 and 4.  I found a .asoundrc that lets me 
use the aliases channel1 and channel2 to address the different inputs, 
and these work fine in darkice.  However, they don't work at the same 
time.  I was running separate instances of darkice, and the second one 
will start, but apparently it can't open the audio device since it's 
locked by the first darkice process, even though it's on a different set 
of inputs.  Is there a good way around this, or does someone have a 
better solution to our broad issue of using icecast as a backup STL?

Thanks,
Joel Ebel