I'm not sure if this has been asked before, but for those who use the DR70D to make 4 channel recordings, what is your method for playing back those four tracks from four separate speakers? I have an A/V receiver with separate analog inputs. But the deck only has stereo out.
You're describing something like Quadrophonic, which was a fad surround-ish technique that required 4 speakers surrounding the listener. There are certain modern surround / ambiance recording techniques that may benefit from similar playback.
Correct me if I'm wrong, but you're not making recordings such as these; you're just using two stereo mic arrays for a concert, correct? I do this sometimes, and you load them into your DAW and mix away but the end result is always a 2-channel stereo file.
The 70D only has the stereo out, and regardless of the number of tracks you have or the configuration of them, that output is being fed a 2-channel stereo mixdown of everything. It's not possible to do what you're suggesting direct from the 70D, but I don't see why you'd want to.