"A soil-less mix fortified with Turface, sand, and granite grit is a good general-purpose mix for many plants," https://nargs.org/reference/troughs#sthash.BOHYRv7e.id21AnuC.dpuf
I've got lots of Turfaceand granite grit, but when I asked for soil-less mix at the nursery, everybody looked blank as if they had never heard of such a thing and said, "I don't think we've ever carried that." We were standing in front of a display of various little (read: expensive) bags of "potting mix." But isn't potting mix (as opposed to potting soil) by definition a soil-less product?
When I lived in another state (it was also in another century) I would buy bulk quantities of a soil-less product called Pro-Mix BX, but I haven't seen it lately. The only bulk mixes my local nursery carries are Berger BM1 and Sungro Professional Growing Mix, and the employees didn't know if they were soil-less.
Can either of these products serve as the base of my planting medium?
I have used Sungro mixes (not the one you mention) with good results. Sungro uses less peat and more bark than some other mixes substituting coir for the peat.
Which Sungro mixes have you used?
It has been several years since I have utilized professional mixes in my small personal nursery but I recall having good results with SunGro general purpose mixes as well as Fafard mixes (I see now they are sold by the same company). My attraction to the SunGro mix I used was the minimal use of peat, so depending on your purposes it seems any of the professional mixes would do. Locally we have a greenhouse supply company that allowed individuals to buy direct rather than pay exorbant inflated prices at retail outlets.