I seriously hate to post this, as the whole subject seems to have been asked to death....
But I'm going to anyway! 

* Followed Art's ummmm...  somewhat questionable directions/instruction sheet.
* I've {bench} hooked everything up from the C6 to the BOB.
* Using a stand alone wall wart for power to the C6.
* I'm getting only about 17mv output from the C6 on X4.
* BOB pin 9 to C6 step
* BOB pin 14 to C6 dir
* ground to...  well, ground!

Clicking spindle on will 'usually' turn on the C6 relay LED. Once. Then it will never turn off until power cycled, or I flip the active hi/low in pins setting.
Thing that looks really odd though, is the output from gnd to pin 9 on the BOB.
I looked at the output on my scope from one of the step pins (2) going to my X while I jogged, then compared it to the step output for comparison.
Pin 2 is +5 and pulsing, but pin 9 is about +1.3 more or less solid. Looked at Mach's diag page, and the row of "LEDs" doesn't have 9 or 14 on. Should it?

I'm ill right now (flu?) - I know there's something simple here.  What have I overlooked?

Well - minor follow up (after an 11hr Nyquil induced coma!).

I unhooked my Z, and hooked the C6 up in it's place.
Now, when I jog (the Z) forward, I get the relay coming on. A slight reverse jog turns the relay off.  Still nothing out the X4 though. 

Also hooked the Z up to pins 8&9 and jogged it up/down no problem. So the pins physically work.

Guess it's looking more like a board issue, so I'll contact (it is Art right?!) at CNC4PC.

Guess it's looking more like a board issue, so I'll contact (it is Art right?!) at CNC4PC.

Mr. Arturo Duncan

OOPS!!    Arturo.  Ok! 

I was close with Art anyhow - at least I didn't call him Jane. 

Well, finally got in touch with Arturo (not Art!).

In a nutshell, the most important part of his reply was:
[Arturo E. Duncan] Please note the C6 does not work with the chineese boards as they deform the waveform.

Guess that's probably my answer!  My BOB came with my motors. And they all came out of....  you guessed it...  China.

I'd already ordered up one of his C10 BOB's a week or two ago, so it's already on it's way here anyhow.  Hopefully that will cure the issue.  
Then I'll relegate my current BOB to extra I/O (as I was going to do with the C10).

Would be nice if that little fact had been mentioned somewhere though.  Like, in any of his documentation.  Anywhere?!

/rant.