OK, here's what I have.
The tablets internal speakers (absolutely crap, the worst sound imaginable) have been removed and the connections to them have been extended and brought outside the tablet.
Connecting DVM Ohms across speaker wires, tablet powered off -
L- and R- 23K
L+ and R+ 23K
L- and L+ 23K
R- and R+ 23K
L- or L+ or R- or R+ to tablet ground 11.5K
So it's definitely a bridged amp, yes? Taking the above 4 speaker outputs I don't have a separate ground connection. Now as you suggested above I understand that I use L+ and R+ and obtain the ground from the tablet ground, thereby having the required L and R outputs with (tablet) ground connection as inputs to my secondary amp with L, R, ground inputs? If that's the case then it makes plenty of sense; I seem to have been assuming this was a much more involved solution...