Gave it another go with markedly different results. They just loaded! Had to rename the files for the P-GRAM+ but it worked. I'm wondering if the problems I was having before might be a result of the card hardware. I recently fried the card, and Marc Hull was generous enough to take a look at it. Other than some cooked voltage regulators / card support chips he noticed a non-standard part (some sort of memory chip) and replaced it with the one actually intended for the card.
Now the card did work before - mostly, as well as any other piece of 30 year old tech...
The RXB2015 version in the zip, is that the most recent?
I have noticed an interesting bug. In RXB's EA - the [D]irectory function works well with DSK and WDS (except hard disk size is represented as an exponent), but not at all with HDX. Seems true of the copy I have on the cart, the version I dumped from the cart to the PGRAM, and the version you just sent which I loaded directly into the PGRAM.
Still pretty awesome - my 8 year old son is learning to program in BASIC using RXB!