Ok that is fine for the frequency as I was wanting to know if you had selected the external controller and you have.
Place this xml in the Mach3 folder and using the laoder open it and see how you get on. I have not changed any ports or pins from that of the original one so not sure if they are correct or not but see how you go.
Hood

OK, I cloned it and used Mach Loader.  Initial error was for different s/n, OK.  Now it gives me  "Spindle-axis Step Port = 0. Valid values are 1 and 2."
"Spindle-axis Dir Port = 0. Valid pin values are 1,23,4,5,6,7,8,9,14,16, and 17" errors.

X,Y,Z,A are step port 1 dir port 1 with 2-9 pins on the axes, and spindle enabled with step pin 14, others zero.
X,Y,Z,A homes are port 1, 10-13, respectively.
EStop is port 1 pin 15.
Outputs port 1 pin 17, port 1 pin 1.
Charge pump port 1 pin 16.

I applied those and it gives me the original spindle errors.  I believe I'm closer to running, though!  What should the inputs be for a relay-based router
as the spindle?  It's not set up yet, physically.

Thanks much for the help, by the way, Hood!

Not sure  why you are cloning it, there is no need to, just open whichever profile you wish to use and set up the ports and pins to what you want and then close, next time you open it will, or at least should, be as you had previously set it up.

Spindle I dont know, never used the G540 but if that is the correct settings then you can tell the SmoothStepper to ignore port and pin errors, do that from Plugin Control menu the SS Config, you should see a box to tick.
Hood

Not sure  why you are cloning it, there is no need to, just open whichever profile you wish to use and set up the ports and pins to what you want and then close, next time you open it will, or at least should, be as you had previously set it up.

Spindle I dont know, never used the G540 but if that is the correct settings then you can tell the SmoothStepper to ignore port and pin errors, do that from Plugin Control menu the SS Config, you should see a box to tick.
Hood

I had cloned it to save the original file intact.  And it was good I had, because before, it had been eating my xml files.   While you were writing the reply, I entered port 2 for the spindle and it saved without error!   I went to the MDI and clicked the REF ALL HOME button and the Z axis started turning at 1.5rps.  I got movement for the first time!

Is there a little G-code test floating around here for testing the axes?  And will I need limit and home switches hooked up to test?

You dont need limit switches but your machine will be safer if you do, especially with you being new. Home switches are a good thing to have as it allows you to set a work offset and then go back to it another time if you restart Mach.
Use one of the wizards to create code, circular pocket wizard might be a good one to try.
Hood

These demos might be handy for testing as well.
http://www.machsupport.com/forum/index.php/topic,18345.0.html
Russ