sock monkey
What's not clear to me is why your asking about interfaces and then saying you don't want it to rely on a computer? Is it you want a dual purpose device? A mixer that is also a interface?
ANd most of the better choices will need an iPad , Tablet or laptop to control. That is how they make them inexpensive. By taking away a lot of unessassary hardware and making it all digital you get a lot more bang for the buck. And as said , that also means less stuff to break.
This is the direction mixers are now going. The release of the Behringer air X series is a good example. Lots of ins and outs, lots of DPS power and so many ways to connect. all for $300. But it is only a 2x USB interface, The Air X18 is the multi channel USB but $800.
 
http://www.behringer.com/EN/Products/Xr12.aspx/
 
And even though most interfaces don't advertise the fact, any interface that is not buss powered is technically a stand alone mixer. My Tascam us1641 certainly outputs to the Monitor outputs all but the SPDIF inputs even with my computer turned off. It might even output to 1/2 but I've not tried that.
I'm pretty sure my Scarlett 6i6 outputs to 1/2 without the computer.
 
 

I will be playing other keyboards live and sometimes with soft synths sometimes without I would to run the hardware through the one piece, instead of out to another mixer then to the various destinations. I thought this was getting to be fairly common.... not sure though.

I would think it depends on at what level your stage set up is. If your in a bar band doing your own sound or even with a house engineer, then multiple outputs would not really be required, just a stereo pair would be all that is needed. In other words, your the one controlling your mix, not a sound man. This is often desirable if the sound man is on the lazy side and not familiar with your material. 
 
If you playing at festivals etc then yes you would want to send more options to the sound man.
 
So don't rule out a small digital mixer with only stereo USB capabilities.
The new Behringers X series are worth a gander.
  http://www.behringer.com/EN/products/X18.aspx
There is also the QSC Touch mix series 
http://qsc.com/products/Mixers/Touchmix_Series/TouchMix-16/