Hey Bill. If you turn the gain on the amp all of the way up you should be able to get enough signal out of the headphone jack on an iPod or phone running straight in. I use a similar scheme in my garage with powered monitors. However as you said there is potential for some awful plug and unplug or other noises.
The easiest simplest route would be to have direct access to the amp and use the sensitivity knobs for the volume. You'll just have to make sure that the gains are down during plug and unplug.