On-Stage Monitor Mixer Design

[Transmogrifox]

I was inspired by a recent thread and thought that such a thing as requested here would be a really useful little utility:
http://www.diystompboxes.com/smfforum/index.php?topic=113021.0

As a result I couldn't help but try to piece something together that does the job well. Here is a link to the design and notes about one possible solution.  Purely schematic/design at this point.  As usual details of power jack connections and input/output connections are not shown.
http://cackleberrypines.net/transmogrifox/TransmogriNotes/stage_mixer/

I went a little overboard on the power amp capability, but then thought this could actually be used as a little mixer & practice amp in 1.  If you have a little 8 ohm or 16 ohm speaker, you can get a couple watts out of this and it has the advantage of the AUX/MP3 input.

Now the trick is to finish building these things I keep thinking up  

Comments/suggestions welcome.  Then maybe it will be improved by the time I actually build it.

[EDIT]...and I got to looking and realized these little class D amplifier chips are pretty cheap for what they do.  Possible to have a 50-Watt amplifier in something the size of a stompbox if adequate power supply is provided (think 19.2V laptop supply):
http://www.mouser.com/ds/2/405/tpa3116d2-556241.pdf [/EDIT]