Ok, this is one of those things that's just better to try out than explain! But the magic words in play were indeed offsets (I was looking for 'homing' related info earlier!)
Anyway, in Mach3 go to the 'offsets' screen & in the X & Y fields, enter the distance from 0,0 set by the homing switches (machine coord home) to the 'middle' of your table.
Now, when you click 'ref all home', your machine still returns to the homing switches, but now once the axis have homed rather than the DRO reading 0,0, they'll now read with whatever your entered offset is offset is (eg on mine when homed the DRO will read X -110, Y -60)
Now click on 'Goto Z' and your table will move rapidy to position 0,0 (which is the middle of your table)...you can load up your G-Code as normal knowing that you can get back to this point in an instant.
Lovely, I have exorcised the DIY CNC
demons....no more worries about having to start from scratch if/when my steppers stall!
PS, Just one thing, apparently the offset settings are only a temp setting in Mach 3.....meaning they'll be lost each time you exit Mach3
To have your machines specific offsets load up everytime you start Mach3, a google search reveals the following workaround (& it might seem a load of old gobbledegook, but it's simple enough to follow with the screen in front of you - & it works)....
"On the offset screen, click "Save Offsets". Scroll down to the last one, G59P253. Set up your X & Y offsets there and save.
Open the General Configuration screen. At the bottom right side, check the box that says "copy G54 from G59.253 at startup". Restart Mach3 and you'll have your G54 offsets."