Thanks, I worked with Thorton's version for a few months. The activity was low as well, great for n-3 and n-2 development. The higher alkaline sodium metaborate may be a better substitute for borax in low action development. I agitated the Thorton D23 normally Decent ASA, 320 for TriX. I'm convinced that triX just isn't absorbing as much developer and needs more activity to get those great midtone/highlight separation I know is possible.
One observation regarding splitting 100g of Sodium Sulfite between A and B bath is the solvent action isn't as pronounced and looks more like Thorton's variation with 85g/liter sodium sulfite rather then straight D23 with 100g/l. I expected the solvent action to be the same as using 100g/l soduim sulfite as in D23 for the same development time. Splitting definitely affected the Sod sulfite's solvent effect on the grain in a way that is less flattering