Each time you purchase same Packed Equipment, sub equipment can be different. I hope, it won't same in all cases either with same vendor or different vendor.
Then, for every PO, in which you buy that packed equipment, you have to maintain the hierarchy. Develop an custom screen by keeping the PO number, Material Code for Packed equipment & by having sub equipment at item level. Keep Description of Sub equipment & qty of sub equipment in Packed equipment (sometimes, more than one). If you use External code for equipment, even you can capture that data in that custom screen.
Use BAPI_EQUI_CREATE to create Sub equipments automatically by assigning the Packed Equipment as Superior Equipment.
I don't see any other solution unless you have material code for sub equipments & mentioning them in PO or creating those sub equipments manually & assigning that to superior equipment.