The BX is definately capable of using a small to medium size PHD. As J-Tres mentions, it's just a matter of auger length and lift height, and not so much a limitation of PTO HP unless you bore out 50 holes a day for a living. Even smaller spec 3PH lifts can handle a PHD such as offered by the <A target="_blank" HREF=http://www.vassarfarmequip.com/catalog/diggers.htm>Vassar Co.</A>. The limitation will be the effective hole depth and possibly auger tip clearance during transport. My Cat 0 445 can use a Vassar PHD but can only dig to a 32" depth at 6", 9", or 12" hole diameters.
The rest of the esteemed denizens know infinately more about B-hoes than I do. [img]/w3tcompact/icons/clever.gif[/img]