it's difficult to slip in a birth pool at home...not enough room! Plus, with SPD you're best on your knees bending over the edge, with the pelvis at its widest and fully supported. Avoid labouring facing out. I waited till the baby had crowned before turning around to have her pulled out (she took too long for me to wait while she kicked at my insides!!). No idea what it's like to birth on land with SPD, I did water both times, on my knees.
Don't be afraid of the SPD during labour. It's the only time in the pg that SPD will actually work FOR you - it's widened your pelvis and is nice and flexy. As long as you're not moving your feet apart during labour - feet planted evenly and only pelvis width apart for rocking and pelvis swinging, for instance. HTH, if not, there's the Pelvic Instability Association you can google