Using a channel driver written about 5 years ago by Bogdan Diaconescu, YO3IIU, I have a pretty clean way of using the on board sound (snd_bcm2835)
You can use a amplified speaker plugged into the 3.5 MM jack on the RPi2 to monitor the node. I've posted the source code at <https://github.com/N4IRS/AllStar/tree/master/chan_alsaradio>

I will update the README over the next couple of days. The only thing I have used the channel driver for, is to monitor the node on a local speaker WITHOUT needing to add a second USB sound device.
On the RPI, this is a one way driver. The on board sound does not have a mic input. From there let you imagination run wild.

Stay tuned to THIS list for more info on the RPi and the ARM boards in general.

73, Steve N4IRS

-- 
"Anything is possible if you don't know what you are talking about."
1st Law of Logic