[Elecraft] Mixer for audio

[G4GNX]

I want to setup an audio mixer facility so that I can have at least on 
stereo headphone output and/or a stereo speaker output. That's the easy end. 
:-)

I want to feed it with inputs from the K3S, IC7100, SDR output from a PC and 
possibly a Wouxun multi-band VHF. So a device with at least 4 stereo inputs 
and appropriate level controls.

Has anyone else done this and can recommend a unit that's as RF proof as 
possible. I'm not averse to using a few ferrites, but the system has to be 
clean with 400W HF near it, as I need to listen to the SDR whilst 
transmitting.

Thoughts on how to connect it would also be appreciated, bearing in mind 
that AFAICR the Wouxun only has a low impedance speaker outlet and all 
others must be stereo.

73,

Alan. G4GNX