The Mac Pro 65lb tower has a Hardware assist that detects memory that is BAD because it generates ECC errors (correctable or not) during the Power-On Self Test. Those modules are marked "Empty" and are not used by the System.
After you power off, you could have added or removed modules, so the test is performed at next Power-On "from scratch". It is possible that these BAD modules will squeak by the next time they are tested.
Any modules I find listed as "Empty" are checked for a Retail Vendor's sticker (in case they have a lifetime warranty). Then they are marked as questionable and set aside for further analysis (because I have a strong interest in these issues). They will NEVER be used as a pair for production again, EVER. At least one of them is BAD.
So, despite my original 10GB showing as 8GB last week (despite checking and moving pairs around on the two memory boards and finding that 1 of the 2 x 1GB original Apple sticks was not working and now getting 10GB - Would you just recommend I remove the original memory and install the new memory (not yet taken out from original Crucial packaging).
I used Onyx software earlier tongiht and I wondered if that had triggered something.
Onyx will not "trigger" anything. The detection is done by Hardware at memory speeds. That detection cannot be made better or worse by anything you run.
Those modules that were bad before will be bad again before long. If you leave them in it increases the chances of a double-bit error, which is not correctable. Your Mac is designed to halt on a kernel panic if that occurs, to avoid poisoning your data.