megotatractor,
From the heft, structure and mounting of the subframe, it appears the digging forces will be dispersed through both the transaxle and the frame of the tractor. With the forward subframe mounts bolted to where the loader supports attach to the tractor frame, the hoe's digging forces would pull on these mounts as well as the subframe mounts attached to the transaxle and axle tubes. It's hard to say how much force the transaxle can handle and remain intact.
Per the instructions, the hoe is designed to be mounted and operated on a tractor with a front-end loader. It appears the weight of the loader would act to counter balance some if not most of the weight of the hoe. In case more weight is needed, I'll toss-in a suitcase weight or two into the FEL bucket, especially if the front end gets light when driving the tractor from the garage to the dig site.
PDe