Barryh,
Have a read through the thread below. I think it may give you a higher confidence in the abilities of your tractor. blackmajicwoman put a Woods BH6000 backhoe on his BX1500. Take a look at the trenches he dug and the stumps he pulled. Now it is true that I have not personally run a sub-compact PHD on a BX1500. In my own mind, I think that if my BX2200 can run a full sized PHD, ultrarunner's BX23 with LP PD10 and downpressure unit drills in serpentine rock with little effort, and blackmajicwoman can do this extensive backhoe work with a BX1500, I have a strong confidence that the BX1500 should have no trouble running a LP PD10 or Gearmore D20 in the soil you describe.
Again, I have not seen the combo, but hopefully these facts can ease your mind about the decision you are trying to make. It is your money, and I understand well not wanting to buy something when you aren't sure it will work. I myself have duripan-the hardest hardpan there is. Shovels and prybars just bounce off it, even when it's had water sitting on it for weeks. I debated for years as to whether a BX with backhoe could dig in it. A TBN neighbor, BX23Barry, brought his tractor over recently, and it did indeed dig in the stuff. That relieved my mind enough to order a Woods BH6000 for my BX2200. So, I agree with your caution. blackmajicwoman has other threads re. his BX1500. You can find those and posts by ultrarunner by using the search function. I hope this extra information is helpful as you try to make the best decision. Here's the main thread with blackmajicwoman's BX1500 and the Woods BH6000 backhoe:
http://www.tractorbynet.com/forums/...500-woods-bh6000.html?highlight=BX1500+BH6000