Praxis BB30 Conversion Bottom Bracket question

Hello all. I have a Cannondale Supersix road bike to which I fitted a Praxis Works conversion bottom bracket, to change it from the original BB30 set-up to run a SRAM GXP crankset. The sram crankset is 39/53, and since I'm getting old I could do with changing it to a compact. I could just buy a GXP compact, but I actually have an old FSA SL-K carbon compact crankset that I ran on another bike with shimano external bb cups. Praxis sell different BB30 converter bottom brackets depending on whether you want to convert to GXP or Shimano standard. So I'm wondering, are these bottom bracket converters completely different, or are they actually the same body, or shell, just with different sized bearings to fit either GXP or Shimano axles? Because of course, buying Shimano-compatible bearings to fit into the existing Praxis unit would proably be cheaper than buying a decent GXP compact crankset! I did once email Praxis to ask this but never got a reply. Anyone have any ideas on this?